Hey guys I am new in this forum so if i posted this question in the wrong section, please notify me. Anyway. My concern here is this. So I am trying to find the RATE OF CHANGE of f from pi to 11pi/6 f(x)= tan x I have attached the part i need help on. Note: This is very simple but there is one step which i don't understand. The part where 11pi/6 - pi = 5pi/6 <----- How is this? Please explain..... thanks in advance.