1. The problem statement, all variables and given/known data basically what the topic states - derive the formula for the derivative of arctan x. 2. Relevant equations d/dx (arctan x) = 1/(1+x^2) 3. The attempt at a solution strange question because we already know the answer. but im not sure how to start this. i know arctan x = y therefore tan y = x but what can i do with this? do i need to draw a right triangle and label all the sides? can someone help me get started? thanks.