Problem 211
Evaluate the integral: I = integral (3x+2)/(2x²+x-3) dx
Evaluate the integral: $$ I = \int \frac{3x+2}{2x^2+x-3}\,dx. $$
Explanation of Method
Factoring the denominator and decomposing into partial fractions reduces the integral to two elementary logarithms.
- Factor $2x^2+x-3=(2x+3)(x-1)$.
- Decompose into partial fractions.
- Integrate term by term and combine logs.
Step 1 · Factor and set up partial fractions
$$ 2x^2+x-3 = (2x+3)(x-1), \qquad \frac{3x+2}{(2x+3)(x-1)} = \frac{A}{2x+3} + \frac{B}{x-1}. $$
Multiplying through: $3x+2=A(x-1)+B(2x+3)$. Setting $x=1$: $5=5B$, so $B=1$. Setting $x=-\tfrac32$: $-\tfrac52=-\tfrac52A$, so $A=1$.
Step 2 · Integrate
$$ I = \int \left(\frac{1}{2x+3} + \frac{1}{x-1}\right) dx = \frac12\ln|2x+3| + \ln|x-1| + C. $$
Step 3 · Combine logarithms
$$ I = \ln\left|(x-1)\sqrt{2x+3}\right| + C. $$
Summary Table
| Coefficient | Value |
|---|---|
| $A$ | $1$ |
| $B$ | $1$ |
Additional Notes
- The domain excludes $x=-3/2$ and $x=1$, the roots of the denominator.
- Because the first partial-fraction term has a linear factor with leading coefficient $2$, its antiderivative picks up a factor of $\tfrac12$: $\int dx/(2x+3)=\tfrac12\ln|2x+3|$, not $\ln|2x+3|$ — a common place to drop a constant when the leading coefficient of a linear factor isn't $1$.
- The result can be checked by differentiating $\ln|x-1|+\tfrac12\ln|2x+3|$: this gives $\tfrac{1}{x-1}+\tfrac{1}{2x+3}=\tfrac{(2x+3)+(x-1)}{(x-1)(2x+3)}=\tfrac{3x+2}{(x-1)(2x+3)}$, matching the integrand since $(x-1)(2x+3)=2x^2+x-3$.
Result
The solution to the integral is:
$$
I = \ln\left|(x-1)\sqrt{2x+3}\right| + C.
$$