ã-Ïï¼Ïã (1/Ï)â«e^(2x)cosnxdx=ã-Ïï¼Ïã [1/(2Ï)]â«cosnxd[e^(2x)]
=ã-Ïï¼Ïã [1/(2Ï)][e^(2x)cosnx-â«e^(2x)d(cosnx)]
=ã-Ïï¼Ïã [1/(2Ï)][e^(2x)cosnx+â«e^(2x)nsinnxdx]
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