So in my math class we're studying derivatives involving ln(), tanh, coth, etc.. I need to say this first. I skipped precalc and trig and went straight to calculus, so whenever I see a trig problem, I can only go off of what I've learned "along the way." This problem has baffled me, please help me out. It seems rather simple in nature so it shouldn't take too long to solve this. 1. The problem statement, all variables and given/known data Find the derivative: y = ln(tan x) 2. Relevant equations So there are a ton of rules involving ln() functions. Here's a couple The derivative (d/dx) of ln(x) = 1/x d/dx of ln[f(x)] = derivative of f(x) over f(x) or f'(x)/f(x) 3. The attempt at a solution So, I learned that in these scenarios, tan x, sec x, sin x, etc. are considered composite functions. So I used f'(x)/f(x) to solve. f(x) is clearly tan x. The book says the derivative of tan x = sec2 x. So I end up with, as my answer sec2 x/ tan x. The back of the book gives 1/(sin x cos x) Am I missing a trigonometric rule here? Did I perform this incorrectly?