cos^2 x + sin^2 x = 1 cot^2 x - csc^2 x = -1 So your answer is -1. To understand how I got these identities, look below. In a right triangle ABC with B=90 degrees, AB^2 + BC^2 = AC^2 (PYTHAGORAS THEOREM) Divide this by AC^2 and BC^2 and substitute the corresponding trigonometric ratios and you get the answer.