theta = arctan(y/(x-1)) and phi = arctan(y/(x+1))

I started off by taking the tangent of each side, which seemed obvious enough. So tan(theta) = y/x-1 and tan(phi) = y/x+1, but now I don't know of any method to isolate just the y and the x. Multiplying x-1 and x+1 to the other side doesn't help matters much, since it just adds an x to the other side that you still can't isolate.

Anybody know how to go about solving this? Thanks.