化简:cos^2(a+45度)-sin^2(a+45度)
cos^2(a+45度)-sin^2(a+45度)
=(cosacos45°-sinasin45°)²-(sinacos45+cosasin45)²
=1/2(cosa-sina)²-1/2(sina+cosa)²
=2sinacosa
=sin2a
最后两步怎么来的0.0