# How To Find The Sin(A+B)=SinA.CosB+CosA.SinB?

1. Jul 12, 2012

### optics.tech

Hi everyone,

I wonder why Sin(A+B)=SinA.CosB+CosA.SinB?

Huygen

2. Jul 12, 2012

### phyzguy

The easiest way to see this is to use Euler's formula:
$$e^{ix} = cos(x) + i sin(x)$$

put in A+B for x, expand it, and collect real and imaginary parts.