化简cos^2(A+15)+cos^2(A-15)-cos30cos2A

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化简cos^2(A+15)+cos^2(A-15)-cos30cos2A
化简cos^2(A+15)+cos^2(A-15)-cos30cos2A

化简cos^2(A+15)+cos^2(A-15)-cos30cos2A
cos^2(A+15)+cos^2(A-15)-cos30cos2A
=(cos(2A+30)+1)/2+(cos(2A-30)+1)-cos30cos2A
=cos30cos2A+1-cos30cos2A
=1

cos^2(A+15)+cos^2(A-15)-cos30cos2A
=(cos(2A+30)+1)/2+(cos(2A-30)+1)/2-cos30cos2A (cos2a=2倍
cosa的平方+1)
=(cos(2A+30)+cos(2A-30))/2-cos30cos2A +1
=1(COS(A+B)+COS(A-B)=2COSACOSB)