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Exercise 381Calculus › Single-variable calculus › Integration › Integration techniquesL1Added 2 Nov 2026

Simplifying and decomposing rational integrands

#partial fractions#rational functions

Statement

Compute
∫x+1x dx,∫xx+1 dx,∫dxx(2−3x).\int\frac{x+1}x\,dx,\qquad\int\frac x{x+1}\,dx,\qquad\int\frac{dx}{x(2-3x)}.

Hint

For the first two, divide. For the third, look for Ax+B2−3x\frac A x+\frac B{2-3x}.

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Solution

First. x+1x=1+1x\frac{x+1}x=1+\frac1x, so the integral is x+ln⁡∣x∣+Cx+\ln|x|+C.

Second. xx+1=1−1x+1\frac x{x+1}=1-\frac1{x+1}, so the integral is x−ln⁡∣x+1∣+Cx-\ln|x+1|+C.

Third. We seek 1x(2−3x)=Ax+B2−3x\frac1{x(2-3x)}=\frac Ax+\frac B{2-3x}, i.e. 1=A(2−3x)+Bx1=A(2-3x)+Bx. Taking x=0x=0 gives A=12A=\frac12; taking x=23x=\frac23 gives B⋅23=1B\cdot\frac23=1, so B=32B=\frac32. Hence
∫dxx(2−3x)=12ln⁡∣x∣+32⋅(−13)ln⁡∣2−3x∣+C=12ln⁡∣x2−3x∣+C.\int\frac{dx}{x(2-3x)}=\frac12\ln|x|+\frac32\cdot\left(-\frac13\right)\ln|2-3x|+C=\frac12\ln\left|\frac x{2-3x}\right|+C.

Remark. Differentiate your answer to check: 12(1x+32−3x)=12⋅2x(2−3x)\frac12\left(\frac1x+\frac3{2-3x}\right)=\frac12\cdot\frac{2}{x(2-3x)} ✓.