Question

If f(x) varies directly with x^2, and f(x) = 75 when x = 5, find the value of f(8).

192

256

25

40

Answer 1

The correct answer option is 192.

Explanation:

We know that f(x) varies directly with
`x^(2)` so we can write it as:

`f(x)` ∝
`x^(2)`

Changing it to an equality by the addition of a constant
`k`:

`f(x) = k.x^(2)`

If f(x) = 75 when x = 5, then we can find the value of k:

`75=k(5)^2`

`k=(75)/(25) =3`

If k = 3, we can find the value of f(8):

`f(8)=3(8)^2`

`f(8)=3*64`

`f(8)=`192