Question

If y varies directly as x2 and y=15 when x =9, find the relationship between x and y

Answer 1

`y=303.75`

Step-by-step explanation:

As y varies directly as
`x^2`,
`y` ∝
`x^2` and we have

`y=kx^2` where k is a constant. As
`y=15` when
`x=2`, we have

`15=k*2^2=4k`

or
`k=(15)/(4) =3.75` and

`y=3.75x^2`

∴ when
`x=9`

`y=3.75*9^2=3.75*81=303.75`

Therefore,
`y=303.75`