已知sina(2a+b)=3sinb,a不等于kπ+π/2,a+b不等于kπ+π/2,k为正整数,求证:tan(a+b)=2tana
问题描述:
已知sina(2a+b)=3sinb,a不等于kπ+π/2,a+b不等于kπ+π/2,k为正整数,求证:tan(a+b)=2tana
答
sin[(a+b)+a]=3sin[(a+b)-a]
sin(a+b)cosa+cos(a+b)sina=3sin(a+b)cosa-3cos(a+b)sina
2sin(a+b)cosa=4cos(a+b)sina
sin(a+b)/cos(a+b)=2sina/cosa
tan(a+b)=2tana