求证tan(x+y)*tan(x-y)=tan^2x-tan^2y/1-tan^2xtan^2y
问题描述:
求证tan(x+y)*tan(x-y)=tan^2x-tan^2y/1-tan^2xtan^2y
答
直接展开,用tan(a+b)=(tana+tanb)/(1-tanatanb)
再用平方差公式