Math Problem Statement

integrate (x^2+2x-25)/((x+2)(x+10)(8x-2)), be sure to plug in roots before expanding to get some constants early

Solution

Let's solve the integral:

x2+2x25(x+2)(x+10)(8x2)dx\int \frac{x^2 + 2x - 25}{(x+2)(x+10)(8x-2)} \, dx

Step 1: Factor the Denominator

The denominator is already factored as:

(x+2)(x+10)(8x2)(x+2)(x+10)(8x-2)

We can simplify 8x28x - 2 to 2(4x1)2(4x - 1) for ease of working.

So the integral becomes:

x2+2x25(x+2)(x+10)2(4x1)dx\int \frac{x^2 + 2x - 25}{(x+2)(x+10)2(4x-1)} \, dx

Step 2: Partial Fraction Decomposition

The next step is to express the integrand as a sum of simpler fractions. We'll decompose the rational function into partial fractions:

x2+2x25(x+2)(x+10)(8x2)=Ax+2+Bx+10+C4x1\frac{x^2 + 2x - 25}{(x+2)(x+10)(8x-2)} = \frac{A}{x+2} + \frac{B}{x+10} + \frac{C}{4x-1}

Step 3: Solve for Constants AA, BB, and CC

Multiply both sides of the equation by the denominator (x+2)(x+10)(8x2)(x+2)(x+10)(8x-2):

x2+2x25=A(x+10)(8x2)+B(x+2)(8x2)+C(x+2)(x+10)x^2 + 2x - 25 = A(x+10)(8x-2) + B(x+2)(8x-2) + C(x+2)(x+10)

Now, plug in values for xx that make the factors x+2x+2, x+10x+10, and 4x14x-1 zero to solve for AA, BB, and CC.

  1. Plugging x=2x = -2: x2+2x25=A(8(2)2)x^2 + 2x - 25 = A(8(-2) - 2) 4425=A(18)A=2518=25184 - 4 - 25 = A(-18) \Rightarrow A = \frac{-25}{-18} = \frac{25}{18}

  2. Plugging x=10x = -10: x2+2x25=B(4(10)1)x^2 + 2x - 25 = B(4(-10) - 1) 1002025=B(41)B=5541100 - 20 - 25 = B(-41) \Rightarrow B = \frac{55}{41}

  3. Plugging x=14x = \frac{1}{4}: x2+2x25=C((14+2)(14+10))x^2 + 2x - 25 = C((\frac{1}{4} + 2)(\frac{1}{4} + 10)) (116+2425)=C((94)(414))C=value(\frac{1}{16} + \frac{2}{4} - 25) = C( \left(\frac{9}{4}\right)(\frac{41}{4}) ) \Rightarrow C=\text{value}

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Math Problem Analysis

Mathematical Concepts

Calculus
Integral Calculus
Partial Fraction Decomposition

Formulas

Partial Fraction Decomposition
Integral of a rational function

Theorems

Partial Fractions Theorem
Fundamental Theorem of Calculus

Suitable Grade Level

Grades 11-12