求证 1-cos2a/sina=2sina

求证 1-cos2a/sina=2sina
求证 1-cos2a/sina=2sina

求证 1-cos2a/sina=2sina
根据三角函数二倍角公式,cos2a=1-2(sina)^2
所以1-cos2a/sina=1-[1-2(sina)^2]/sina=1-1+2sina=2sina