tan@*tan2@/(tan2@-tan@)
=1/[(tan2@-tan@)/(tan2@*tan@)]
=1/[1/tan@-1/tan2@]
=1/[1/tan@-(1-tan^2 @)/(2*tan@)]
=1/[(2-1+tan^2 @)/(2*tan@)]
=2*tan@/[1+tan^2 @]
=sin2@
本是万能公式的变通
1/tan2@=(1+tan^2 @)/(2*tan@)
对正切万能公式等式左右取倒数
“tan^2 @”表示“(tan@)^2”
手机不便输入希腊字母,用“@”代替.