As a hint: it might help to draw a right triangle, label the three sides (using a, b, and c, for example), and calculate the tangent for the two non-right angles in the triangle. These will automatically be complementary angles, since (if we label them as A and B) we have A + B + 90 = 180, which simplifies to A + B = 90.
Once you calculate tan(A) and tan(B), you can compare these two expressions and see how they're related.