If f(x) varies directly with x2, and f(x) = 75 when x = 5, find the value of f(8). 40 256 25 192

f(8) = 192

Explanation:
f(x) varies directly with x²
This means that:
f(x) = kx²
where k is the constant of proportionality.

Now, we are given that:
f(x) = 75 at x = 5
Substitute to get k as follows:
f(x) = kx²
75 = k(5)²
75 = 25k
k = 3

This means that the equation is:
f(x) = 3x²

Now, to find f(x) at x = 8, all we have to do is substitute with x = 8 in the equation as follows:
f(8) = 3*(8)²
f(8) = 3*64
f(8) = 192

Hope this helps :)