Question

HELP PLEASE!!!
Write the function that models the relationship. Find z when x = 4 and y = 8.
z varies jointly with x and y. When x = 2 and y = 2, z = 7.

I'm a bit behind in alg 2 and I have to complete a study guide for a test tomorrow and I'm stuck on this question! Help would be much appreciated!
(I know that the answer is z = 7/4xy, but I don't know how to get there.)

Answer 1

do u know what is mean by joint variation ?

Answer 2

it's when one quantity varies directly with 2 or more quantities?

Answer 3

yeah... then
\[z \ \ \ \alpha \ \ xy\]

Answer 4

since you have the equation jus fill in what you have

Answer 5

so.. u can write it as
z = k xy

Answer 6

u've know the values of x and y when z = 7

Answer 7

z = 7
x = 2
y = 2

Answer 8

so it would be 7 = k(2)(2)?

Answer 9

well, k(4)

Answer 10

and u
know that
z = k xy
use the above values and find k

Answer 11

yes!

Answer 12

then k will equal to..
7 = 4k
k = 7/4

Answer 13

now...
write the equation
z = k xy
substituting the value for k and that;s the equation u want...!!

Answer 14

wow okay that was so much easier than i thought! thank you so much! ^_^

Answer 15

now.. to find z when
x= 4 and y = 8
plug those value to the equation u got.. it;s that simple :)

Answer 16

u r welcome!