Question

化简：cos²(A+15°)+cos²(A-15°)-cos30°cos2A.

Answer 1

解析:原式=［1+cos2(A+15°)+1+cos2(A-15°)］-cos2A

=［2+cos(2A+30°)+cos(2A-30°)］-cos2A

=(2+2cos2Acos30°)-cos2A=1+cos2A-cos2A

=1.