Math Problem Statement

Find the result of the definite integral from 0 to 2 of (6x / (x^2 + 6x + 8)) dx.

Solution

The question in the image asks to find the result of the integral:

026xx2+6x+8dx\int_0^2 \frac{6x}{x^2 + 6x + 8} \, dx

Let's solve this step-by-step:

Step 1: Factor the denominator

First, we factor the quadratic expression in the denominator:

x2+6x+8=(x+2)(x+4)x^2 + 6x + 8 = (x + 2)(x + 4)

So the integral becomes:

026x(x+2)(x+4)dx\int_0^2 \frac{6x}{(x + 2)(x + 4)} \, dx

Step 2: Use Partial Fraction Decomposition

We need to express the integrand in terms of partial fractions. Let:

6x(x+2)(x+4)=Ax+2+Bx+4\frac{6x}{(x + 2)(x + 4)} = \frac{A}{x + 2} + \frac{B}{x + 4}

Multiplying both sides by (x+2)(x+4)(x + 2)(x + 4) to clear the denominators:

6x=A(x+4)+B(x+2)6x = A(x + 4) + B(x + 2)

Now, expand the right-hand side:

6x=A(x)+4A+B(x)+2B6x = A(x) + 4A + B(x) + 2B 6x=(A+B)x+(4A+2B)6x = (A + B)x + (4A + 2B)

Step 3: Set up the system of equations

Equating the coefficients of like terms:

  1. For the xx-terms: A+B=6A + B = 6
  2. For the constant terms: 4A+2B=04A + 2B = 0

Step 4: Solve for AA and BB

From the second equation, solve for AA:

4A+2B=02A+B=0B=2A4A + 2B = 0 \quad \Rightarrow \quad 2A + B = 0 \quad \Rightarrow \quad B = -2A

Substitute B=2AB = -2A into the first equation:

A2A=6A=6A=6A - 2A = 6 \quad \Rightarrow \quad -A = 6 \quad \Rightarrow \quad A = -6

Then substitute A=6A = -6 into B=2AB = -2A:

B=2(6)=12B = -2(-6) = 12

Step 5: Rewrite the integral

Now that we have A=6A = -6 and B=12B = 12, we can rewrite the integrand as:

026x+2+12x+4dx\int_0^2 \frac{-6}{x + 2} + \frac{12}{x + 4} \, dx

Step 6: Integrate term by term

The integral of 1x+a\frac{1}{x + a} is lnx+a\ln|x + a|. Therefore, we integrate each term:

026x+2dx=6lnx+202=6(ln(4)ln(2))=6ln(2)\int_0^2 \frac{-6}{x + 2} \, dx = -6 \ln|x + 2| \Big|_0^2 = -6 (\ln(4) - \ln(2)) = -6 \ln(2) 0212x+4dx=12lnx+402=12(ln(6)ln(4))=12ln(32)\int_0^2 \frac{12}{x + 4} \, dx = 12 \ln|x + 4| \Big|_0^2 = 12 (\ln(6) - \ln(4)) = 12 \ln\left(\frac{3}{2}\right)

Step 7: Combine the results

Now combine the two parts:

6ln(2)+12ln(32)-6 \ln(2) + 12 \ln\left(\frac{3}{2}\right)

This simplifies to:

6ln(2)+12(ln(3)ln(2))=6ln(2)+12ln(3)12ln(2)=18ln(2)+12ln(3)-6 \ln(2) + 12 (\ln(3) - \ln(2)) = -6 \ln(2) + 12 \ln(3) - 12 \ln(2) = -18 \ln(2) + 12 \ln(3)

Step 8: Evaluate the expression

Plugging in approximate values for the logarithms:

ln(2)0.6931,ln(3)1.0986\ln(2) \approx 0.6931, \quad \ln(3) \approx 1.0986

We get:

18(0.6931)+12(1.0986)=12.4758+13.1832=0.7074-18(0.6931) + 12(1.0986) = -12.4758 + 13.1832 = 0.7074

Thus, the value of the integral is approximately 0.7070.707.

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Math Problem Analysis

Mathematical Concepts

Definite Integrals
Partial Fraction Decomposition
Logarithms
Quadratic Factoring

Formulas

Integral of 1 / (x + a) is ln|x + a|
Partial fraction decomposition for rational functions

Theorems

Fundamental Theorem of Calculus

Suitable Grade Level

Grades 11-12