Answer to Question #52640 in Trigonometry for libv

Question

what is the actual value of , arc tan [(-1)/(1)] , arc tan [(1)/(-1)] . do they have different value? then why ? both looks like arc tan [-1] which is -pi/4 . so now what is the actual value of arc sin [(-15)/(17)] , arc tan [(15)/(-17)] . do they have different value like arc tan or do they have same value ? then why ???