Question:

Given that $\displaystyle y$ varies directly as the square of $\displaystyle x$ and that $\displaystyle y=12$ when $\displaystyle x=2$, find

(a) the equation relating $\displaystyle x$ and $\displaystyle y$

(b) the values of $\displaystyle x$ when $\displaystyle y=-27$

My solution: (a)

$\displaystyle y=k(x^2)$

$\displaystyle k=y/x^2$

$\displaystyle =12/2^2$

$\displaystyle =12/4$

$\displaystyle =3$

$\displaystyle y=3x^2$

(b)

$\displaystyle -27=3x^2$

$\displaystyle x^2=-27/3$

$\displaystyle =-9$

$\displaystyle x= ?$

How do I solve for (b)?

Thanks