hey people, i have a question asking me to sketch the level curves of this scalar field:

T(x,y) = (2x-y)/(x^2+y^2), for T = -1,-.5,0,.5 and 1.

The theory we were taught was to let T equal a constant and then rearrange the equation to find y in terms of x, but you cannot simply rearrange this equation like that. I know i must have done something like this before, it seems pretty familiar, but it's bugging me :P can someone lend a hand?