厦门长庚医院挂号官网:cos(A+B)cos(A-B)化简的结果是( )
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cos(A+B)cos(A-B)化简的结果是( )
A.cos^2A-sin^2B
B.sin^2A-sin^2B
C.cos^2A-cos^2B
D.sin^2A-COS^2B
怎么作的?
A.cos^2A-sin^2B
B.sin^2A-sin^2B
C.cos^2A-cos^2B
D.sin^2A-COS^2B
怎么作的?
cos(A+B)cos(A-B)
=(cosAcosB-sinAsinB)*(cosAcosB+sinAsinB)
=cos^2Acos^2B-sin^2Asin^2B
=cos^2Acos^2B-(1-cos^2A)*(1-cos^2B)
=cos^2A+(cos^2B-1)
=cos^2A-sin^2B
选A.
cos(A+B)cos(A-B)化简的结果是( )
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