∫1/(x^100+x)dx ∫1/(e^x+e^3x)dx

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∫1/(x^100+x)dx∫1/(e^x+e^3x)dx∫1/(x^100+x)dx∫1/(e^x+e^3x)dx∫1/(x^100+x)dx∫1/(e^x+e^3x)dx1、∫1/(x^100+x

∫1/(x^100+x)dx ∫1/(e^x+e^3x)dx
∫1/(x^100+x)dx ∫1/(e^x+e^3x)dx

∫1/(x^100+x)dx ∫1/(e^x+e^3x)dx
1、
∫1/(x^100+x)dx
=∫1/x - x^98/(x^99+1) dx
=∫1/x dx - ∫x^98 /(x^99+1) dx
=lnx - 1/99 *∫ 1/(x^99+1) d(x^99)
=lnx -1/99 *ln|x^99+1| +C C为常数
2、
∫1/(e^x+e^3x)dx
=∫1/[e^x *(e^2x+1)] dx
=∫ [1/e^x - e^x/(e^2x+1)] dx
= -e^(-x) - ∫1/(e^2x+1) d(e^x)
= -e^(-x) - arctan(e^x) +C C为常数