If a and b are the measures of two first quadrant angles and sin a = and sin b = ,

Question

find sin (a + b).

Answer 1

Use the identity:

sin(a+b)=sin(a)cos(b)+cos(a)sin(b)

Good to know also:
sin(a-b)=sin(a)cos(b)-cos(a)sin(b)
cos(a+b)=cos(a)cos(b)-sin(a)sin(b)
cos(a-b)=cos(a)cos(b)+sin(a)sin(b)

Answer 2

Use the addition formula:

sin(a+b)=SinACosB+sinBcosA

cosA= sqrt (1-sin^2 A)
cosB= sqrt (1-sin^2 B)