Sum To Product恆等式

參考 > 代數: 三角恆方程

描述

\(\sin{x}+\sin{y}=2\sin{(\frac{x+y}{2})}\cos{(\frac{x-y}{2})}\)

\(\sin{x}-\sin{y}=2\cos{(\frac{x+y}{2})}\sin{(\frac{x-y}{2})}\)

\(\cos{x}+\cos{y}=2\cos{(\frac{x+y}{2})}\cos{(\frac{x-y}{2})}\)

\(\cos{x}-\cos{y}=2\sin{(\frac{x+y}{2})}\sin{(\frac{x-y}{2})}\)