Math Problem Statement

\displaystyle\int\dfrac{3x^3-5x^2+10x-3}{3x+1},dx=

Solution

To solve the integral

I=3x35x2+10x33x+1dxI = \int \dfrac{3x^3 - 5x^2 + 10x - 3}{3x + 1} \, dx

we can start by performing polynomial division on the rational function 3x35x2+10x33x+1\dfrac{3x^3 - 5x^2 + 10x - 3}{3x + 1}.

Step 1: Perform Polynomial Division

We divide 3x35x2+10x33x^3 - 5x^2 + 10x - 3 by 3x+13x + 1.

  1. Divide the leading term of the numerator 3x33x^3 by the leading term of the denominator 3x3x, which gives x2x^2.

  2. Multiply x2x^2 by 3x+13x + 1, giving 3x3+x23x^3 + x^2.

  3. Subtract (3x3+x2)(3x^3 + x^2) from (3x35x2)(3x^3 - 5x^2), resulting in 6x2+10x-6x^2 + 10x.

  4. Divide 6x2-6x^2 by 3x3x, which gives 2x-2x.

  5. Multiply 2x-2x by 3x+13x + 1, giving 6x22x-6x^2 - 2x.

  6. Subtract (6x22x)(-6x^2 - 2x) from (6x2+10x)(-6x^2 + 10x), resulting in 12x312x - 3.

  7. Divide 12x12x by 3x3x, which gives 44.

  8. Multiply 44 by 3x+13x + 1, giving 12x+412x + 4.

  9. Subtract (12x+4)(12x + 4) from (12x3)(12x - 3), resulting in 7-7.

Thus, the polynomial division gives us:

3x35x2+10x33x+1=x22x+473x+1\dfrac{3x^3 - 5x^2 + 10x - 3}{3x + 1} = x^2 - 2x + 4 - \dfrac{7}{3x + 1}

Step 2: Integrate Each Term

Now we integrate term by term:

  1. (x22x+4)dx=x33x2+4x+C1\int (x^2 - 2x + 4) \, dx = \dfrac{x^3}{3} - x^2 + 4x + C_1

  2. 73x+1dx\int -\dfrac{7}{3x + 1} \, dx

    We can use substitution for this integral. Let u=3x+1u = 3x + 1, so du=3dxdu = 3 dx. This gives:

    73x+1dx=731udu=73lnu+C2=73ln3x+1+C2\int -\dfrac{7}{3x + 1} \, dx = -\dfrac{7}{3} \int \dfrac{1}{u} \, du = -\dfrac{7}{3} \ln |u| + C_2 = -\dfrac{7}{3} \ln |3x + 1| + C_2

Step 3: Combine Results

Combining all terms, we get the final result:

I=x33x2+4x73ln3x+1+CI = \dfrac{x^3}{3} - x^2 + 4x - \dfrac{7}{3} \ln |3x + 1| + C

where C=C1+C2C = C_1 + C_2 is the constant of integration.


Do you want more details or have any questions?

Here are 5 related questions to expand on this topic:

  1. How does polynomial long division work, and why is it useful for integration?
  2. Can we apply synthetic division for polynomials like these?
  3. What is the role of substitution in integrals involving logarithms?
  4. How would the integral change if we had a different denominator, such as 3x+23x + 2?
  5. Can you explain partial fraction decomposition and when it's applicable?

Tip: When dealing with rational functions, always consider polynomial division or partial fraction decomposition before integrating!

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Math Problem Analysis

Mathematical Concepts

Integral Calculus
Polynomial Division
Substitution Method
Logarithmic Integration

Formulas

Polynomial Division: f(x) / g(x) = quotient + remainder / g(x)
Substitution: ∫f(u) du = F(u) + C
Logarithmic Integration: ∫(1/u) du = ln|u| + C

Theorems

Fundamental Theorem of Calculus
Logarithmic Integral Theorem

Suitable Grade Level

Undergraduate Level - Calculus 1