证明:sinπ/9[(sinπ/9)+sin(3π/9)]=sin2(2π/9)

问题描述:

证明:sinπ/9[(sinπ/9)+sin(3π/9)]=sin2(2π/9)
等号后边是sin平方(2π/9)

此题用到和差化积公式和倍角公式和差化积公式:sin(a+b)+sin(a-b)=2sina*cosb,也可写成sina+sinb=22sin(a+b)/2*cos(a-b)/2倍角公sin(2a)=2sina*cosa套用公式即可解题如下:sinπ/9[(sinπ/9)+sin(3π/9)...