Giải thích các bước giải:
Ta có:
\(\begin{array}{l}
{\sin ^2}x - {\sin ^2}y\\
= \left( {\sin x - \sin y} \right)\left( {\sin x + \sin y} \right)\\
= 2.\cos \frac{{x + y}}{2}.\sin \frac{{x - y}}{2}.2.\sin \frac{{x + y}}{2}.cos\frac{{x - y}}{2}\\
= \left( {2.\sin \frac{{x + y}}{2}.\cos \frac{{x + y}}{2}} \right).\left( {2.\sin \frac{{x - y}}{2}.\cos \frac{{x - y}}{2}} \right)\\
= \sin \left( {x + y} \right).\sin \left( {x - y} \right)\,\,\,\,\,\,\left( {\sin 2x = 2\sin x.\cos x} \right)
\end{array}\)
