tan(a+b)=(tan(a)+tan(b))/(1-tan(a)*tan(b))tan(a-b)=(tan(a)-tan(b))/(1+tan(a)*tan(b)) tan(a+b) = (tan(a) + tan(b)) / (1 - tan(a)*tan(b)) tan(a-b) = (tan(a) - tan(b)) / (1 + tan(a)*tan(b))