Hi! I have a question about approximation of functions with small angles. I was looking through some notes from my teacher and didnt understand why the following approximation is valid. We have a system which is at equlibrium at an angle, say a. Now we wanted to se what happens with the equilibrim if we deviate from a, with a small angle say, n. All the calculations isnt necessary here so i cut them out. He chooses to write cos(a+n) = cosa * cos n - sina * sin n, just by expanding. However for sin(a + n) he just writes sin(a+n) = sin(a) Can you please validate this and tell me why this is ok to do? I mean why we dont expand sin(a+n) in the same manner?