In the range is it solvable? Or are there values of theta when the equations are not solvable?
Assuming you mean to solve for x and y, just treat and as constants. In particular, you can multiply the first equation by , the second equation by , and add the equations to eliminate y. A system of equations would be "non-solvable" if and only if the resulting coefficient of x were 0. But a rather nice thing happens here!