∫cos(2x+1)^5dx=?

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∫cos(2x+1)^5dx=?

∫cos(2x+1)^5dx=?
∫cos(2x+1)^5dx=?

∫cos(2x+1)^5dx=?
5/16 *sin(2x+1)+5/96 *sin[3(2x+1)]+1/160 *sin[5(2x+1)]

∫[cos(2x+1)]^5dx
= (1/2)∫ [cos(2x+1)]^4 d sin(2x+1)
=(1/2)∫ {1-2(sin(2x+1))^2+ [sin(2x+1)]^4} d sin(2x+1)
=(1/2)[ sin(2x+1) - 2(sin(2x+1))^3/3 + [sin(2x+1)]^5/5 ] +C

给一个通用解法,可以对任意的∫cos^mxdx来解
首先给一个小公式:
∫cos^m(x)dx=∫cos^(m-1)(x)d(sinx)=sinxcos^(m-1)x+∫(m-1)sin^2xcos^(m-2)xdx
=sinxcos^(m-1)x+∫(m-1)(1-cos^2x)cos^(m-2)xdx
=sinxcos^(m-1)x+∫(m-1)cos^(m-2...

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给一个通用解法,可以对任意的∫cos^mxdx来解
首先给一个小公式:
∫cos^m(x)dx=∫cos^(m-1)(x)d(sinx)=sinxcos^(m-1)x+∫(m-1)sin^2xcos^(m-2)xdx
=sinxcos^(m-1)x+∫(m-1)(1-cos^2x)cos^(m-2)xdx
=sinxcos^(m-1)x+∫(m-1)cos^(m-2)xdx-∫(m-1)cos^m(x)dx
也就是
∫cos^m(x)dx=1/msinxcos^(m-1)x+(m-1)/m∫cos^(m-2)xdx
∫cos(2x+1)^5dx
=1/2∫cosu^5du u=2x+1
=1/10sinucos^4u+2/5∫cos^3udu (用到上面的小公式)
=1/10sinucos^4u+2/15sinucos^2u+4/15∫cosudu
=1/10sinucos^4u+2/15sinucos^2u+4/15sinu
=1/10sin(2x+1)cos^4(2x+1)+2/15sin(2x+1)cos^2(2x+1)+4/15sin(2x+1)+C

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