The image contains several mathematics problems. We will solve problem number 8 which asks us to find the integral $J = \int \frac{6x^2 + 4x}{x^3 + x^2 - x - 1} dx$.

AnalysisIntegrationPartial FractionsCalculusDefinite Integral
2025/5/18

1. Problem Description

The image contains several mathematics problems. We will solve problem number 8 which asks us to find the integral J=6x2+4xx3+x2x1dxJ = \int \frac{6x^2 + 4x}{x^3 + x^2 - x - 1} dx.

2. Solution Steps

First, factor the denominator.
x3+x2x1=x2(x+1)(x+1)=(x21)(x+1)=(x1)(x+1)(x+1)=(x1)(x+1)2x^3 + x^2 - x - 1 = x^2(x+1) - (x+1) = (x^2 - 1)(x+1) = (x-1)(x+1)(x+1) = (x-1)(x+1)^2.
Then we can rewrite the integral as:
J=6x2+4x(x1)(x+1)2dxJ = \int \frac{6x^2 + 4x}{(x-1)(x+1)^2} dx.
We can use partial fraction decomposition to split the fraction into simpler terms:
6x2+4x(x1)(x+1)2=Ax1+Bx+1+C(x+1)2\frac{6x^2 + 4x}{(x-1)(x+1)^2} = \frac{A}{x-1} + \frac{B}{x+1} + \frac{C}{(x+1)^2}
6x2+4x=A(x+1)2+B(x1)(x+1)+C(x1)6x^2 + 4x = A(x+1)^2 + B(x-1)(x+1) + C(x-1)
6x2+4x=A(x2+2x+1)+B(x21)+C(x1)6x^2 + 4x = A(x^2 + 2x + 1) + B(x^2 - 1) + C(x-1)
6x2+4x=Ax2+2Ax+A+Bx2B+CxC6x^2 + 4x = Ax^2 + 2Ax + A + Bx^2 - B + Cx - C
6x2+4x=(A+B)x2+(2A+C)x+(ABC)6x^2 + 4x = (A+B)x^2 + (2A+C)x + (A-B-C)
Comparing coefficients:
A+B=6A+B = 6
2A+C=42A+C = 4
ABC=0A-B-C = 0
From the first equation, we have B=6AB = 6-A.
From the third equation, we have C=AB=A(6A)=2A6C = A-B = A-(6-A) = 2A-6.
Substituting CC into the second equation:
2A+2A6=42A + 2A - 6 = 4
4A=104A = 10
A=104=52A = \frac{10}{4} = \frac{5}{2}.
B=652=12252=72B = 6 - \frac{5}{2} = \frac{12}{2} - \frac{5}{2} = \frac{7}{2}.
C=2(52)6=56=1C = 2(\frac{5}{2}) - 6 = 5-6 = -1.
Thus, we have
6x2+4x(x1)(x+1)2=5/2x1+7/2x+1+1(x+1)2\frac{6x^2 + 4x}{(x-1)(x+1)^2} = \frac{5/2}{x-1} + \frac{7/2}{x+1} + \frac{-1}{(x+1)^2}.
Now we can rewrite the integral:
J=(5/2x1+7/2x+11(x+1)2)dxJ = \int \left( \frac{5/2}{x-1} + \frac{7/2}{x+1} - \frac{1}{(x+1)^2} \right) dx
J=521x1dx+721x+1dx1(x+1)2dxJ = \frac{5}{2} \int \frac{1}{x-1} dx + \frac{7}{2} \int \frac{1}{x+1} dx - \int \frac{1}{(x+1)^2} dx
J=52lnx1+72lnx+1+1x+1+CJ = \frac{5}{2} \ln|x-1| + \frac{7}{2} \ln|x+1| + \frac{1}{x+1} + C

3. Final Answer

J=52lnx1+72lnx+1+1x+1+CJ = \frac{5}{2} \ln|x-1| + \frac{7}{2} \ln|x+1| + \frac{1}{x+1} + C

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