Posted by Jay on .
z varies directly as x^2. If z=36 when x=3,find zwhen x=4.

algebra 
Reiny,
z varies directly as x^2 > z = kx^2 , where k is a constant
if z=36, x = 3
336 = k(9)
k = 4
so y = 4x^2
when x=4 , y = 4(16) = 64
or , by ratio ....
z1/z2 = x1^2/x2^2
z1/36 = 4^2/3^2
z1 = 36(16/9) = 64