Question

If f(x) varies directly with x2, and f(x) = 72 when x = 6, find the value of f(3).

A.
18

B.
54

C.
36

D.
108

Answer 1

f(x) = Kx^2
72 = K6^2
K = 72/6^2 = 2
f(x) = 2x^2
f(3) = 2*3^2
f(3) = 18

Answer 2

So its 18?

Answer 3

Yes it's 18