Answer:
jamal traveled 5 hours at 55mph and 4 hours at 60mph
Step-by-step explanation:
time x will be time jamal travels 55 mph (in hours)
time y will be time jamal travels 60 mph (in hours)
distanced traveled 520 miles
distance = time*speed
520= x*55+y*60
520=55x+60y
jamal traveled for 9 hours
9 hours is composed to the two times x and y
9=x+y
then
x=9-y
substitute into 520=55x+60y
520=55(9-y)+60y
520=495-55y+60y
520=495+5y
25=5y
y=5
x+y=9
x+5=9
x=4
time x is time jamal travels 55 mph (in hours)
time y is time jamal travels 60 mph (in hours)
jamal traveled 5 hours at 55mph and 4 hours at 60mph
In a random sample of 205 people, 149 said that they watched educational television. Find the 95% confidence interval of the true proportion of people who watched educational television. Round intermediate answers to at least five decimal places.
Answer: Given a sample of 200, we are 90% confident that the true proportion of people who watched educational TV is between 72.1% and 81.9%.
Step-by-step explanation:
[tex]\frac{154}{200} =0.77[/tex]
[tex]1-0.77=0.23[/tex]
[tex]\sqrt{\frac{(0.77)(0.23)}{200} }[/tex]=0.049
0.77±0.049< 0.819, 0.721
What is lim x → 0 e^2x - 1/ e^x - 1
Hello, please consider the following.
[tex]\displaystyle \forall x \in \mathbb{R}\\\\\dfrac{e^{2x}-1}{e^x-1}\\\\=\dfrac{(e^x)^2-1^2}{e^x-1}\\\\=\dfrac{(e^x-1)(e^x+1)}{e^x-1}\\\\=e^x+1\\\\\text{So, we can find the limit.}\\\\\lim_{x\rightarrow 0} \ {\dfrac{e^{2x}-1}{e^x-1}}\\\\=\lim_{x\rightarrow 0} \ {e^x+1}\\\\=e^0+1\\\\\large \boxed{\sf \bf \ =2 \ }[/tex]
Thank you
What type of counting problem is this?
Johnny is a very picky eater, so he likes to use a lot of condiments. He has ketchup, salt, pepper, and shredded cheese at his disposal. His mother tells him he may only make two additions to his meal (i.e., he can add condiments only twice, regardless of whether or not he already used them). How many different ways can Johnny improve his meal?
A.Combination with repetition
B.Combination without repetition
C.Permutation with repetition
D.Permutation without repetition
Answer:
option A
Step-by-step explanation:
Permutation is An arrangement of objects in an ORDER
but combination is the opposite.
In this question, There is a combination! I hope this helped! have a great day!4 Points] Under the HMM generative model, what is p(z1 = z2 = z3), the probability that the same die is used for the first three rolls? b. [4 Points] Suppose that we observe the first two rolls. What is p(z1 = 1 | x1 = 2, x2 = 4), the probability that the casino used the fair die in the first roll?
Answer:
Step-by-step explanation:
We first examine a simple hidden Markov model (HMM). We observe a sequence of rolls of a four-sided die at an "occasionally dishonest casino", where at time t the observed outcome x_t Element {1, 2, 3, 4}. At each of these times, the casino can be in one of two states z_t Element {1, 2}. When z_t = 1 the casino uses a fair die, while when z_t = 2 the die is biased so that rolling a 1 is more likely. In particular: p (x_t = 1 | z_t = 1) = p (x_t = 2 | z_t = 1) = p (x_t = 3 | z_t = 2) = p (x_t = 4 | z_t = 1) = 0.25, p (X_t = 1 | z_t = 2) = 0.7, p (X_t = 2 | z_t = 2) = p (X_t = 3 | z_t = 2) = p (X_t = 4 | z_t = 2) = 0.1. Assume that the casino has an equal probability of starting in either state at time t = 1, so that p (z1 = 1) = p (z1 = 2) = 0.5. The casino usually uses the same die for multiple iterations, but occasionally switches states according to the following probabilities: p (z_t + 1 = 1 | z_t = 1) = 0.8, p (z_t = 2) = 0.9. The other transition probabilities you will need are the complements of these. a. Under the HMM generative model, what is p (z1 = z2 = z3), the probability that the same die is used for the first three rolls? b. Suppose that we observe the first two rolls. What is p (z1 = 1 | x1 = 2, x2 = 4), the probability that the casino used the fair die in the first roll? c. Using the backward algorithm, compute the probability that we observe the sequence x1 = 2, x2 = 3, x3 = 3, x4 = 3 and x5 = 1. Show your work (i.e., show each of your belief for based on time). Consider the final distribution at time t = 6 for both p (z_t = 1) = p (z_t = 2) = 1.
ANSWER:
Let say we have that the first state of the die is state 1. Therefore the probability of this is p(z1=1)=0.5.
Also the probability that the same die is used(i.e. casino would be in the same state) is p(z2=1|z1=1)=0.8.
Again, suppose the first state of the die is state 2. So, p(z1=2)=0.5 and p(z2=2|z1=2)=0.9.
Other transition probabilities can be written as
p(zt+1=2|zt=1)=1-p(zt+1=1|zt=1)=.2
p(zt+1=1|zt=2)=1-p(zt+1=2|zt=2)=.1
p(z3=1|z1=1) = [p(z3=1|z2=2)*p(z2=2|z1=1)]+[p(z3=1|z2=1)*p(z2=1|z1=1)] = 0.1*0.2+0.8*0.8 = 0.66
p(z3=2|z1=2) = [p(z3=2|z2=2)*p(z2=2|z1=2)]+[p(z3=2|z2=1)*p(z2=1|z1=2)] = 0.9*0.9+0.2*0.1 = 0.83
With this, the total probability that the same die is used for the first three rolls (i.e. casino would be in the same state) is given thus;
{p(z1=1)*p(z3=1|z1=1)}*{p(z1=2)*p(z3=2|z1=2)}
= 0.5*0.66+0.5*0.83 = 0.745
Prob = 0.745
Beginning 177 miles directly north of the city of Morristown, a van travels due west. If the van is travelling at a speed of 31 miles per hour, determine the rate of change of the distance between Morristown and the van when the van has been travelling for 71 miles. (Do not include units in your answer, and round to the nearest hundredth.)
Answer:
Step-by-step explanation:
From the given information;
let the hypotenuse be a , the opposite which is the north direction be b and the west direction which is the adjacent be c
SO, using the Pythagoras theorem
a² = c² + 177²
By taking the differentiation of both sides with respect to time t , we have
[tex]2a \dfrac{da}{dt} = 2c \dfrac{dc}{dt} + 0[/tex]
[tex]\dfrac{da}{dt} = \dfrac{c}{a} \dfrac{dc}{dt}[/tex]
At c = 71 miles,[tex]a = \sqrt{ (71)^2 +(177)^2}[/tex]
[tex]a = \sqrt{ 5041+31329}[/tex]
[tex]a = \sqrt{ 36370}[/tex]
a = 190.71
SImilarly, [tex]\dfrac{dc}{dt} = \ 31 miles \ / hr[/tex]
Thus, the rate of change of the distance between Morristown and the van when the van has been travelling for 71 miles can be calculate as:
[tex]\dfrac{da}{dt} = \dfrac{c}{a} \dfrac{dc}{dt}[/tex]
[tex]\dfrac{da}{dt} = \dfrac{71}{190.71} \times 31[/tex]
[tex]\dfrac{da}{dt} = 0.37229 \times 31[/tex]
[tex]\mathbf{\dfrac{da}{dt} = 11.54}[/tex] to the nearest hundredth.
The isotope of plutonium 238Pu is used to make thermoelectric power sources for spacecraft. Suppose that a space probe was launched in 2012 with 4.0 kg of 238Pu.
Required:
a. If the half-life of 238Pu is 87.7 yr, write a function of the form Q(t)= Q0e- kt.to model the quantity Q(t) of 238Pu left after t-years.
b. If 1.6 kg of 238Pu is required to power the spacecraft's data transmitter, for how long will scientists be able to receive data?
Answer:
A) Q(t) = 4e^-(0.0079t)
B) t = 115.99 ≈ 116
Therefore scientist will be able to receive data after 116 years
Step-by-step explanation:
a)
to write a function of the form Q(t)= Q₀e⁻^kt to model the quantity Q(t) of ²³⁸Pu left after t-years.
so given that; half-life of ²³⁸Pu is 87.7 years,
∴ t = 87.7 years , Q(t) = 0.5Q₀
Now we substitute these value in the form Q(t)= Q₀e⁻^kt
Q(t)= Q₀e⁻^kt
0.5Q₀ = Q₀e^ -(87.7k)
0.5 = e^ -(87.7k)
now we take the natural logarithm of both sides
In(0.5) = Ine^ -(87.7k)
Now using the property logₙnᵃ = a
-87.7k = In(0.5)
k = - In(0.5) / 87.7
k = 0.0079
ALSO it was given that Q₀ = 4.0 kg
Therefore , model quality Q(t) of ²³⁸pu left after t years is:
Q(t) = 4e^-(0.0079t)
b)
to find the time left after 1.6kg of ²³⁸pu
we simple substitute Q(t) = 1.6 into Q(t) = 4e^-(0.0079t)
so we have
1.6 = 4e^-(0.0079t)
e^-(0.0079t) = 1.6/4
e^-(0.0079t) = 0.4
again we take the natural logarithm of both sides,
Ine^-(0.0079t) = In(0.4)
again using the property logₙnᵃ = a
-0.0079t = In(0.4)
t = - in(0.4) / 0.0079
t = 115.99 ≈ 116
Therefore scientist will be able to receive data after 116 years
If “n” is a positive integer divisible by 3 and n is less than or equal to 44, then what is the highest possible value of n?
Answer:
Step-by-step explanation:
positive integer divisible by 3 includes
3,6,9,12,15,18,21,24,27,30,33,36,39,42,45...
less than highest possible value is 42
Each student in a school was asked, "What is your favorite color?" The circle graph below shows how they answered
Which color was chosen by approximately one fourth of the students?
Approximately what percentage of the students chose purple or green?
Answer:
a). BLUE color
b). 20%
Step-by-step explanation:
a). "Which color was chosen by approximately one fourth of the students?"
Since one fourth of the students will be represented by one fourth area of the circle given.
That means color of choice represented by the quarter of the circle will be the color liked by one fourth students.
In the figure attached, BLUE color is the choice of one fourth students in the class.
b). Area represented by purple, green and other colors is a quarter of the circle.
If we divide this quarter into five equal sections, then the total of purple and green will be [tex]4\times \frac{1}{5}[/tex] of the the quarter of the circle.
Measure of the angle defined by purple or green sections = [tex]\frac{4}{5}\times 90[/tex]
= 72°
Percentage of the students who preferred purple or green = [tex]\frac{72}{360}\times 100[/tex]
= 20%
Answer:
blue
20%
Step-by-step explanation:
56 x 10^-4)
Group of answer choices
2.37 x 10^-16
4.21 x 10^15
2.4 x 10^-16
4.2 x 10^15
9514 1404 393
Answer:
(d) 4.2×10^15
Step-by-step explanation:
Your calculator will tell you the quotient is about ...
4.21348...×10^15
The least precise number in the division is 1.5, which has 2 significant digits. Therefore, the result should be rounded to 2 significant digits:
4.2×10^15
Need help with this as soon as possible pls
Answer:
i think
x=6.77
y=11.33
Find the final amount in each of these retirement accounts, in which the rate
of return on the account and the regular contribution change over time,
(a) $400 per month invested at 4%, compounded monthly, for 10 years, then
$600 per month invested at 6%, compounded monthly, for 10 years
(b) $1,000 per quarter invested at 4.42%, compounded quarterly, for 10 years,
then $1,500 per quarter invested at 7.4%, compounded quarterly, for 15
years
Answer:
Compound Interest: The future value (FV) of an investment of present value (PV) dollars earning interest at an annual rate of r compounded m times per year for a period of t years is:
FV = PV(1 + r/m)mt
or
FV = PV(1 + i)n
where i = r/m is the interest per compounding period and n = mt is the number of compounding periods.
One may solve for the present value PV to obtain:
PV = FV/(1 + r/m)mt
Numerical Example: For 4-year investment of $20,000 earning 8.5% per year, with interest re-invested each month, the future value is
FV = PV(1 + r/m)mt = 20,000(1 + 0.085/12)(12)(4) = $28,065.30
Notice that the interest earned is $28,065.30 - $20,000 = $8,065.30 -- considerably more than the corresponding simple interest.
Effective Interest Rate: If money is invested at an annual rate r, compounded m times per year, the effective interest rate is:
reff = (1 + r/m)m - 1.
This is the interest rate that would give the same yield if compounded only once per year. In this context r is also called the nominal rate, and is often denoted as rnom.
Numerical Example: A CD paying 9.8% compounded monthly has a nominal rate of rnom = 0.098, and an effective rate of:
r eff =(1 + rnom /m)m = (1 + 0.098/12)12 - 1 = 0.1025.
Thus, we get an effective interest rate of 10.25%, since the compounding makes the CD paying 9.8% compounded monthly really pay 10.25% interest over the course of the year.
Mortgage Payments Components: Let where P = principal, r = interest rate per period, n = number of periods, k = number of payments, R = monthly payment, and D = debt balance after K payments, then
R = P × r / [1 - (1 + r)-n]
and
D = P × (1 + r)k - R × [(1 + r)k - 1)/r]
Accelerating Mortgage Payments Components: Suppose one decides to pay more than the monthly payment, the question is how many months will it take until the mortgage is paid off? The answer is, the rounded-up, where:
n = log[x / (x – P × r)] / log (1 + r)
where Log is the logarithm in any base, say 10, or e.
Future Value (FV) of an Annuity Components: Ler where R = payment, r = rate of interest, and n = number of payments, then
FV = [ R(1 + r)n - 1 ] / r
Future Value for an Increasing Annuity: It is an increasing annuity is an investment that is earning interest, and into which regular payments of a fixed amount are made. Suppose one makes a payment of R at the end of each compounding period into an investment with a present value of PV, paying interest at an annual rate of r compounded m times per year, then the future value after t years will be
FV = PV(1 + i)n + [ R ( (1 + i)n - 1 ) ] / i
where i = r/m is the interest paid each period and n = m × t is the total number of periods.
Numerical Example: You deposit $100 per month into an account that now contains $5,000 and earns 5% interest per year compounded monthly. After 10 years, the amount of money in the account is:
FV = PV(1 + i)n + [ R(1 + i)n - 1 ] / i =
5,000(1+0.05/12)120 + [100(1+0.05/12)120 - 1 ] / (0.05/12)
PLEASE HELP ASAP WILL GIVE BRAINLIEST
A bag contains three red marbles, two green ones, one lavender one, two yellows, and two orange marbles. HINT [See Example 7.] How many sets of seven marbles include at least one yellow one but no green ones
Answer: 8
Step-by-step explanation:
Given: A bag contains three red marbles, two green ones, one lavender one, two yellows, and two orange marbles.
Total marbles other than green = 8
Total marbles other than green and yellow = 6
Then the number of sets of seven marbles include at least one yellow one but no green ones:-
[tex]^{2}C_1\times^{6}C_6+ ^2C_2\times^6C_5\\\\= 2\times 1+1\times6\\\\=2+6=8[/tex]
Number of sets of seven marbles include at least one yellow one but no green ones = 8
An economist is interested in studying the spending habits of consumers in a particular region. The population standard deviation is known to be $1,000. A random sample of 50 individuals resulted in an average expense of $15,000. What is the width of the 99% confidence interval for the mean of expense? a. 364.28 b. 728.55 c. 329.00 d. 657.99
Answer:
The width is [tex]w = \$ 729.7[/tex]
Step-by-step explanation:
From the question we are told that
The population standard deviation is [tex]\sigma = \% 1,000[/tex]
The sample size is [tex]n = 50[/tex]
The sample mean is [tex]\= x = \$ 15,000[/tex]
Given that the confidence level is 99% then the level of significance is mathematically represented as
[tex]\alpha = 100 - 99[/tex]
=> [tex]\alpha = 1\%[/tex]
=> [tex]\alpha = 0.01[/tex]
Next we obtain the critical value of [tex]\frac{\alpha }{2}[/tex] from the normal distribution table, the value is
[tex]Z_{\frac{\alpha }{2} } = Z_{\frac{0.01 }{2} } = 2.58[/tex]
Generally margin of error is mathematically represented as
[tex]E = Z_{\frac{\alpha }{2} * \frac{\sigma }{\sqrt{n} }[/tex]
substituting values
[tex]E = 2.58 * \frac{1000 }{\sqrt{50} }[/tex]
[tex]E = 2.58 * \frac{1000 }{\sqrt{50} }[/tex]
[tex]E = 364.9[/tex]
The width of the 99% confidence interval is mathematically evaluated as
[tex]w = 2 * E[/tex]
substituting values
[tex]w = 2 * 364.9[/tex]
[tex]w = \$ 729.7[/tex]
According to a report in USA Today, more and more parents are helping their young adult children purchase their first home. Suppose eight persons in a random sample of 40 young adults who recently purchased a home in Kentucky received help from their parents. You have been asked to construct a 95% confidence interval for the population proportion of all young adults in Kentucky who received help from their parents. What is the margin of error for a 95% confidence interval for the population proportion
Answer:
the margin of error
= 1.96 x 0.0632
= 0.124
Step-by-step explanation:
this question has the sample size, n = 40
8 people have received help from their parents from this sample.
8/40 = 0.2
which is the sample proportion
z = 1 - 0.2
= 0.8
to calculate standard error
√pz/n
= √0.2 x 0.8/40
= √0.16/40
= 0.0632
at 95% confidence level
z(alpha/2) = 1.96
therefore the margin of error
= 1.96 x 0.0632
= 0.124
Ayudaaaaaaaa plorafacvor
4/24,7/5,5/3,3/5 espero hallude
Write the equation in slope-intercept form. y = 7(x + 2) + 3x
Step-by-step explanation:
y=mx+c
where m=7(x+2)and c=3xAnswer:
y= 10x +14
Step-by-step explanation:
Distribute parenthesis:
7(x+2) + 3x = 7x +14 +3x
Then combine like terms:
7x + 3x = 10x +14
pls help! I need the answer quickly! thank you!
Answer:
C) 82/2
Step-by-step explanation:
The area of a square is calculated by multiplying a side by itself
so one side of the square is 9 in
the area of a triangle is calculated by multiplying height and base and that divided by 2
since E is the midpoint, if we draw a line show the height from there
the height would be 9
9*9/2 = 82/2
A prism and two nets are shown below: Prism 1 E 3 Net A Net Part A: Which is the correct net for the prism? Explain your answer. (2 points) Part B: Write the measurements of Sides AB. BC, and CD of the correct net. (4 points) Part C: What is the surface area of the prism? Show your work. (4 points)
Answer:
A) Net A (see explanation)
B) AB = 3 in. | BC = 5 in. | CD = 7.2 in.
C) SA = 98.4 in²
Step-by-step explanation:
Part A
Net A is the correct net for the prism. If you look at the way the folds are, the flaps on the top and bottom would fold up to make the side of the prism. On net B, the flaps wouldn’t fit the shape correctly.
Part B
AB = This is the height of the prism.
= 3 in.
BC = This is the slant on the front of the prism.
= 5 in.
CD = This is the length of the prism.
= 7.2 in.
Part C
* First we’ll solve for the two triangles. They are the same shape and size, so we just need to solve one then duplicate it.
One triangle:
A = 1/2bh
= 1/2 (4) (3)
= 6 in²
Back rectangle:
A = bh
= 7.2 (3)
= 21.6 in²
Front rectangle:
A = bh
= 7.2 (5)
= 36 in²
Bottom rectangle:
A = bh
= 7.2 (4)
= 28.8 in²
Total:
A = 6 + 6 + 21.6 + 36 + 28.8
= 98.4 in²
why infinity ( ) can’t be included in an inequality?
Answer:
Step-by-step explanation:
Because then the value on the other side will be unbounded by the infinity sign while expressing the answers on a number line.
please click thanks and mark brainliest if you like :)
A poker hand consisting of 7 cards is dealt from a standard deck of 52 cards. Find the probability that the hand contains exactly 3 face cards. Leave your answer as a reduced fraction.
Answer:
The probability is 2,010,580/13,378,456
Step-by-step explanation:
Here is a combination problem.
We want to 7 cards from a total of 52.
The number of ways to do this is 52C7 ways.
Also, we know there are 12 face cards in a standard deck of cards.
So we are selecting 3 face cards from this total of 12.
So also the number of cards which are not face cards are 52-12 = 40 cards
Out of all these 40, we shall be selecting exactly 4. The number of ways to do this 40C4
Thus, the required probability will be;
(40C4 * 12C3)/52C7 = (91,390 * 220)/133,784,560
= 20,105,800/133,784,560 = 2,010,580/13,378,456
Use the following conversions to answer the question.
60 seconds = 1 minute
60 minutes = 1 hour
24 hours = 1 day
How many minutes are there in a week?
A. 420
B. 1,400
C. 10,080
D. 604,800
Answer:
C. 10,080
Step-by-step explanation:
We can multiply to find how many minutes there are in 1 day.
24 * 60 = 1,440
Now, we can multiply that value by 7 to find out how many minutes there are in 1 week.
1,440 * 7 = 10,080
Best of Luck!
A survey of undergraduates revealed the follwoing information: WOMEN MENsample mean weight 124.7 183.3sample standard deviation of weight 23.32 25.41sample proportion Roman Catholic 0.40 0.32Sample mean GPA 3.34 3.24Sample standard deviation of GPA 0.35 0.44Sample size 20 25Assume the populations are normally distributed. Suppose you want to determine whether the proportion of SCU women who are Roman Catholic is greater than the proportion of SCU men that are Roman Catholic.a. What are the null and alternative hypothesis to run this test?b. What is the calculated value of the test statistic?c. What is the p-value of the calculated test statistic?d. What is the conclusion of the hypothesis test, at 5% the significance level?
Answer:
the answers are below:
Step-by-step explanation:
a. null hypothesis:
H0: Pw - Pm = 0 (so Pw = Pm)
alternate hypothesis:
H1: Pw - Pm > 0 (so Pw > Pm)
where Pw is the proportion of women
Pm is the proportion of men
b.) proportion of women = o.40
proportion of men = 0.32
sample size of women = 20
sample size of men = 25
[tex]z = 0.4 - 0.32/ \sqrt{((0.4 *0.6)/20) * (0.32 * 0.68)/25)}[/tex]
[tex]z = 0.56[/tex]
c.) p value =
p(z>0.56)
= 0.7123
= 1 - 0.7123
= o.2877 which can be approximated to be 0.288
d. alpha value was set at 0.05
the p value is greater than alpha.
therefore it is not statistically significant.
we conclude that the proportion of roman catholic women is not greater than men.
Which expression represents the perimeter of the rectangle above? . 6x + 3. 10x + 6. 8x² + 6x. 12x + 6
There is no any image of rectangle
[tex] {4}^{3} [/tex]
evaluate this expression
Answer:
64
Step-by-step explanation:
Answer:
64
Step-by-step explanation:
4^3
= 4 * 4 * 4
= 16 * 4
= 64
explain why the APR does not compare loans for different lengths of time
Answer:
APR does not tell you how long your rate is locked for. A 15-year loan may have a lower interest rate, but could have a higher APR, since the loan fees are amortized over a shorter period of time. It is not wise to compare a 30-year loan with a 15-year loan using their respective APRs.
Step-by-step explanation:
Please answer fast! :)
Answer:
D
Step-by-step explanation:
The fastest way to solve this probelm would be to plug in each x value into these equations untill it outputs the correct two y values.
When you plug 3 into equation D the entire right side it will become.
y-1=0
y=1, which is true.
When you plug 6 into that equation.
y-1=5
y=6 which is also true.
im sorry but the thing is i cant translate these words but the answer is D
The length of a rectangle is three times its width. If the perimeter of the rectangle is 160 cm, what are the dimensions of this rectangle?
Answer:
The dimensions or Area of the rectangle is 1200cm².
What requirements are necessary for a normal probability distribution to be a standard normal probability distribution? Choose the correct answer below. A. The mean and standard deviation have the values of and B. The mean and standard deviation have the values of and C. The mean and standard deviation have the values of and D. The mean and standard deviation have the values of and
Answer:
In order for a Normal Probability Distribution to be a Standard Normal Probability Distribution, the mean and standard deviation must have the values of µ = 0 and σ = 1.
Where µ refers to the Mean of the distribution and σ refers to the standard deviation.
µ is pronounced 'mu' and σ is pronounced sigma.
Cheers!
Find the maximum rate of change of f at the given point and the direction in which it occurs. f(x, y) = 8 sin(xy), (0, 9)
Answer:
The maximum rate of change of f at (0, 9) is 72 and the direction of the vector is [tex]\mathbf{\hat i}[/tex]
Step-by-step explanation:
Given that:
F(x,y) = 8 sin (xy) at (0,9)
The maximum rate of change f(x,y) occurs in the direction of gradient of f which can be estimated as follows;
[tex]\overline V f (x,y) = \begin {bmatrix} \dfrac{\partial }{\partial x } (x,y) \hat i \ + \ \dfrac{\partial }{\partial y } (x,y) \hat j \end {bmatrix}[/tex]
[tex]\overline V f (x,y) = \begin {bmatrix} \dfrac{\partial }{\partial x } (8 \ sin (xy) \hat i \ + \ \dfrac{\partial }{\partial y } (8 \ sin (xy) \hat j \end {bmatrix}[/tex]
[tex]\overline V f (x,y) = \begin {bmatrix} (8y \ cos (xy) \hat i \ + \ (8x \ cos (xy) \hat j \end {bmatrix}[/tex]
[tex]| \overline V f (0,9) |= \begin {vmatrix} 72 \hat i + 0 \end {vmatrix}[/tex]
[tex]\mathbf{| \overline V f (0,9) |= 72}[/tex]
We can conclude that the maximum rate of change of f at (0, 9) is 72 and the direction of the vector is [tex]\mathbf{\hat i}[/tex]