z varies jointly with y and the square of x. If z=256 when y=-8 and x=-4, find z when x=-3 and y=-4.

Answer 1

z = k y x^2
256 = k (-8)(16)
k = 256 / -128 = -2
so
z = -2 y x^2
= -2 * -3 * 16

Answer 2

z=ky*x^2
256=k(-8)(4)^2 solve for k.
then find z when x=-3, y=-4. K is a constant, and does not change.

Answer 3

whoops -2 * -4 * 9

Answer 4

z = kyx^2
That is,
z/(yx^2) = k, a constant. So, you want z such that
z/(-4*9) = 256/(-8*16)