## Precalculus (6th Edition)

$-2\sin 11.5^{o}\cdot\cos 36.5^{o}$
Sum-to-Product: $\displaystyle \sin A+\sin B=2\sin(\frac{A+B}{2})\cos(\frac{A-B}{2})$ $\sin(-A)=-\sin A$ ---------- $\displaystyle \frac{A+B}{2}=\frac{25^{o}+(-48)^{o}}{2}=-11.5^{o}$ $\displaystyle \frac{A-B}{2}=\frac{25^{o}-(-48)^{o}}{2}=36.5^{o}$ $\sin 25^{o}+\sin(-48^{o})=2\sin(-11.5^{o})\cdot\cos(36.5^{o})$ $=-2\sin 11.5^{o}\cdot\cos 36.5^{o}$