
Stephen C. answered 07/20/19
SAT Math, Algebra, Trig, PreCalc Tutor
But note that, for most values of A and B, sin(A+B) does NOT equal sin A + sin B.
(Try A and B of 90 degrees, for example).
That is, sin(A+B) = sin A + sin B is NOT a trig identity.
Another quick way to determine whether this is a trig identity or not is to note that the range of sin(A+B) is [-1,1], but the range of sin A + sin B is [-2,2].