Maths Question: $\text{Show that }\sin 8x+\sin 10x=2\sin 9x\cos x$ Maths Solution: $\sin x+\sin 10x=2\sin \tfrac{8x+10x}{2}\cos \tfrac{10x-8x}{2}=2\sin 9x\cos x$ University mathstopic: Trigonometry III
