Hi

I am having trouble with the following question:

How would you change the following equation in r and $\displaystyle \theta $ to an equivalent equation in x and y?

$\displaystyle r=2sin2\theta$

Another question:

$\displaystyle r=tan\theta$

$\displaystyle \sqrt{x^2+y^2}=\frac{y}{x}$

$\displaystyle x(x+y)=y$

$\displaystyle x^2+xy=y$

what have i done wrong

P.S