证明cos²(A+B)—sin²(A—B)=cos2Acos2B

问题描述:

证明cos²(A+B)—sin²(A—B)=cos2Acos2B

左边=(cosAcosB-sinAsinB)²-(sinAcosB-cosAsinB)²=cos²Acos²B + sin²Asin²B - 2sinAsinBcosAcosB - sin²Acos²B - cos²Asin²B + 2sinAsinBcosAcosB=cos²Acos...