PART 11：積化和差 例題1

求 \(\sin {82.5^ \circ }\cos {37.5^ \circ } = ?\)

SOL:

\(\sin {82.5^ \circ }\cos {37.5^ \circ } = \frac{1}{2}\left( {\sin {{120}^ \circ } + \sin {{45}^ \circ }} \right)\)  \( = \frac{1}{2}\left( {\frac{{\sqrt 3 }}{2} + \frac{{\sqrt 2 }}{2}} \right)\)