求证 sin~4a-cos~4a=sin~2a-cos~2a tan~2asin~2a=tan~2a-sin~2a
问题描述：
求证 sin~4a-cos~4a=sin~2a-cos~2a tan~2asin~2a=tan~2a-sin~2a
答
sin^4a-cos^4a
=(sin^2a-cos^2a)(sin^2a+cos^2a)
=(sin^2a-cos^2a)*1=sin^2a-cos^2a
tan^2asin^2a=(sce^2a-1)sin^2a
=tan^2a-sin^2a