第1个回答 2019-10-14
用泰勒公式直接展开就可以了本回答被提问者采纳
第2个回答 2019-10-15
1-cosxcos2xcos3x
=1-(1/2)*(cos3x+cosx)cos3x
=1-(1/2)*(cos3x)^2-(1/2)*cosxcos3x
=1-(1/4)*(1+cos6x)-(1/4)*(cos4x+cos2x)
=3/4-(1/4)*cos6x-(1/4)*cos4x-(1/4)*cos2x
=(1/4)*[(1-cos6x)+(1-cos4x)+(1-cos2x)]
~(1/4)*[(1/2)*36x^2+(1/2)*16x^2+(1/2)*4x^2]
=7x^2
所以a=7，n=2
=1-(1/2)*(cos3x+cosx)cos3x
=1-(1/2)*(cos3x)^2-(1/2)*cosxcos3x
=1-(1/4)*(1+cos6x)-(1/4)*(cos4x+cos2x)
=3/4-(1/4)*cos6x-(1/4)*cos4x-(1/4)*cos2x
=(1/4)*[(1-cos6x)+(1-cos4x)+(1-cos2x)]
~(1/4)*[(1/2)*36x^2+(1/2)*16x^2+(1/2)*4x^2]
=7x^2
所以a=7，n=2