Solve[ForAll[{x, y}, Equivalent[ m (x/a) + n (y/b) == 1, ((t1 - t2) (b (-1 + t1 t2) x + a (b + b t1 t2 - (t1 + t2) y)))/((1 + t1^2) (1 + t2^2)) == 0]], {m, n}, Reals] // Simplify

The code generates an answer containing "if". How can I remove the "if" part to obtain the result shown in the bottom image?
