sin(2a)[cot(a/2)-tan(a/2)]=4cos^2(a)求证,
问题描述：
sin(2a)[cot(a/2)-tan(a/2)]=4cos^2(a)求证,
答
sin(2a)[cot(a/2)-tan(a/2)]=sin(2a)*[cos(a/2)/sin(a/2) - sin(a/2)/cos(a/2)]=2sina*cosa*[cos²(a/2) - sin²(a/2)]/[sin(a/2)*cos(a/2)]=4sin(a/2)*cos(a/2)*cosa*cosa/[sin(a/2)*cos(a/2)]=4cos²(...