Math Problem Statement

Evaluate the integral ∫ (4x + 7) / (2x^2 + x - 1) dx.

Solution

The integral presented in the image is:

4x+72x2+x1dx\int \frac{4x + 7}{2x^2 + x - 1} \, dx

To solve this integral, we can try to decompose the fraction using partial fraction decomposition or attempt a substitution.

Step-by-step solution:

  1. Recognize the form: The denominator is a quadratic expression 2x2+x12x^2 + x - 1, which suggests we could attempt a substitution or factor the quadratic, if possible.

  2. Substitute: Let u=2x2+x1u = 2x^2 + x - 1. Then, compute dudu: ddx(2x2+x1)=4x+1.\frac{d}{dx}(2x^2 + x - 1) = 4x + 1.

    Now, rewrite the integral in terms of uu.

    The expression 4x+74x + 7 can be written as: 4x+7=(4x+1)+6.4x + 7 = (4x + 1) + 6.

    So, the integral becomes: 4x+12x2+x1dx+62x2+x1dx.\int \frac{4x+1}{2x^2 + x - 1} \, dx + \int \frac{6}{2x^2 + x - 1} \, dx.

  3. Simplify each part:

    • For the first part 4x+12x2+x1dx\int \frac{4x+1}{2x^2 + x - 1} \, dx, since 4x+1=du/dx4x+1 = du/dx, this simplifies to: duu=lnu=ln2x2+x1.\int \frac{du}{u} = \ln |u| = \ln |2x^2 + x - 1|.

    • For the second part 62x2+x1dx\int \frac{6}{2x^2 + x - 1} \, dx, we will likely need to complete the square in the quadratic and then use a standard arctangent or logarithmic integration method.

      Completing the square for 2x2+x12x^2 + x - 1 gives: 2(x+14)298.2\left(x + \frac{1}{4}\right)^2 - \frac{9}{8}. From here, a standard arctangent substitution can be applied.

Result:

Thus, the integral of the expression can be split into two parts: one involving a logarithm and another likely involving an arctangent.

Would you like the detailed completion of the second part of the integral?


Here are some related questions you could explore:

  1. How does partial fraction decomposition work for rational functions?
  2. How can completing the square help in solving integrals involving quadratics?
  3. What is the method of substitution in integration, and when is it most useful?
  4. How do you solve integrals involving arctangent functions?
  5. What are the general techniques for solving rational integrals?

Tip: Completing the square is a very useful technique when integrating expressions involving quadratic polynomials in the denominator. It simplifies many integrals into standard forms.

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Math Problem Analysis

Mathematical Concepts

Integral Calculus
Partial Fraction Decomposition
Substitution in Integration
Completing the Square

Formulas

∫ f'(x) / f(x) dx = ln |f(x)| + C
Quadratic formula ax^2 + bx + c = 0
Completing the square for ax^2 + bx + c

Theorems

Fundamental Theorem of Calculus
Method of Substitution

Suitable Grade Level

College Level Calculus