Question

If f(x) varies directly with x2 and f(x)=10 what is the value of f(x) when x=3

Answer 1

If f(x) varies directly with  $x^2$

If f(x) varies directly with x then we use equation f(x) = kx

where k is the constant of proportionality

So equation becomes $f(x) = kx^2$

We use the information and find out k

f(x)= 10

$f(x) = kx^2$

$10= kx^2$

$k = \frac{10}{x^2}$

now we use the value of k and find the value of f(x) when x=3

$f(x) = \frac{10}{x^2}*x^2$

f(x) = 10

The value of f(x) = 10 when x= 3