Question

what is sin 20 degrees cos 10 degrees + cos 20 degrees sin 10 degrees

Answer 1

$$\begin{gathered} \sin 20°\times \cos 10°+\cos 20°\times \sin 10° \\ =\sin \left(20°+10°\right)\left[\mathbf{as}\mathbf{,}\mathbf{}\mathbf{sin}\mathbf{}\mathbf{A}\mathbf{}\mathbf{cos}\mathbf{}\mathbf{B}\mathbf{}\mathbf{+}\mathbf{}\mathbf{cos}\mathbf{}\mathbf{A}\mathbf{}\mathbf{sin}\mathbf{}\mathbf{B}\mathbf{}\mathbf{=}\mathbf{}\mathbf{sin}\mathbf{}\left(\mathbf{A}\mathbf{+}\mathbf{}\mathbf{B}\right)\right] \\ =\sin 30° \\ =\frac{1}{2}\left[\mathbf{as}\mathbf{,}\mathbf{}\mathbf{sin}\mathbf{}\mathbf{30}\mathbf{°}\mathbf{}\mathbf{=}\mathbf{}\frac{\mathbf{1}}{\mathbf{2}}\right] \end{gathered}$$