求不定积分∫sin(3x)sin(5x)dx,求详细过程~

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求不定积分∫sin(3x)sin(5x)dx,求详细过程~
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求不定积分∫sin(3x)sin(5x)dx,求详细过程~
求不定积分∫sin(3x)sin(5x)dx,求详细过程~

求不定积分∫sin(3x)sin(5x)dx,求详细过程~
sin(3x)sin(5x)
=sin(4x-x)sin(4x+x)
=(sin4xcosx-cos4xsinx)*(sin4xcosx+cos4xsinx)
= sin^4x-sin^x
=(1-cos8x)/2-(1-cosx)/2
=(cos2x-cos8x)/2
所以∫sin(3x)sin(5x)dx=sin2x/4-sin8x/16+C

积化和差就可以了。化为余弦差

利用三角函数积化和差公式。
∫sin(3x)sin(5x)dx
=1/2∫(cos2x-cos8x)dx
=1/2(∫cos2xdx-∫cos8xdx)
=1/4sin4x-1/16sin8x+C

sin(3x