Trigonometry Identities - Product to Sum to Identity (Degrees)

Question

Complete the product to sum identity for this expression

$$	ext{cos}{(60^{\circ})}	ext{cos}{(135^{\circ})}$$

Accepted Answer

$$=\frac{1}{2} \left[   	ext{cos}(60^{\circ} - 135^{\circ}) +  	ext{cos}(60^{\circ} + 135^{\circ})  ight]$$

Answer

$$=\frac{1}{2} \left[   	ext{sin}(60^{\circ} + 135^{\circ}) +  	ext{sin}(60^{\circ} - 135^{\circ})  ight]$$