证明一:(cosa-1)^2+sin^2a=2-2cosa
问题描述:
证明一:(cosa-1)^2+sin^2a=2-2cosa
答
(cosa-1)^2+sin^2a
=cos^2a-2cosa+1+sin^2a
=sin^2a+cos^2a+1-2cosa
=2-2cosa