I have these two equations
$$u = \frac{2x}{x^2 + y^2} \\ v = \frac{-2y}{x^2 + y^2}$$
And I need to put $x$ in terms of $u$ and $v$. If I take polar co-ordinates and plug them in I get(in the case of $u$), because
(rcos(theta))^2 + (rsin(theta))^2 = 1
$$u = 2r\cos(\theta)$$
Can I simply change that back to
$$u = 2x$$
?