## Addition and Subtraction Formulas for Sine and Cosine IV

$2\cos\alpha\cos\beta=\cos (\alpha+\beta)+\cos (\alpha-\beta)\\ 2\sin\alpha\cos\beta=\sin (\alpha+\beta)+\sin (\alpha-\beta)$

Summary. We present a wordless proof of two basic trigonometric identities involving two angles, sine, and cosine.

### References

1. J. Molokach, , The College Mathematics Journal, MAA, May 2016 (47), n 3, 199