Math Problem Statement

Decompose the expression \(\frac{2x - 3}{x^2 + x - 6}\).

Solution

To decompose the given expression 2x3x2+x6\frac{2x - 3}{x^2 + x - 6}, let's proceed with the following steps:

  1. Factorize the Denominator: The denominator is x2+x6x^2 + x - 6. We need to factorize this quadratic expression. We look for two numbers that multiply to 6-6 and add up to 11 (the coefficient of xx).

    x2+x6=(x+3)(x2)x^2 + x - 6 = (x + 3)(x - 2)

    So, the expression becomes:

    2x3(x+3)(x2)\frac{2x - 3}{(x + 3)(x - 2)}

  2. Attempt Partial Fraction Decomposition: Since the numerator 2x32x - 3 has a lower degree than the denominator (x+3)(x2)(x + 3)(x - 2), we can decompose it into partial fractions:

    2x3(x+3)(x2)=Ax+3+Bx2\frac{2x - 3}{(x + 3)(x - 2)} = \frac{A}{x + 3} + \frac{B}{x - 2}

  3. Solve for A and B: To find AA and BB, multiply both sides by the denominator (x+3)(x2)(x + 3)(x - 2):

    2x3=A(x2)+B(x+3)2x - 3 = A(x - 2) + B(x + 3)

    Expand and collect like terms:

    2x3=Ax2A+Bx+3B2x - 3 = Ax - 2A + Bx + 3B

    Combine terms involving xx:

    2x3=(A+B)x+(2A+3B)2x - 3 = (A + B)x + (-2A + 3B)

    Now, equate the coefficients for xx and the constant terms:

    • For xx: A+B=2A + B = 2
    • For the constant: 2A+3B=3-2A + 3B = -3
  4. Solve the System of Equations: From the equations:

    • A+B=2A + B = 2
    • 2A+3B=3-2A + 3B = -3

    Solving these, we get:

    • Multiply the first equation by 2: 2A+2B=42A + 2B = 4
    • Add this to the second equation: (2A2A)+(2B+3B)=43(2A - 2A) + (2B + 3B) = 4 - 3

    So, 5B=1B=155B = 1 \Rightarrow B = \frac{1}{5}.

    Substitute B=15B = \frac{1}{5} into A+B=2A + B = 2:

    A+15=2A=215=1015=95A + \frac{1}{5} = 2 \Rightarrow A = 2 - \frac{1}{5} = \frac{10 - 1}{5} = \frac{9}{5}

  5. Final Decomposition: Substitute AA and BB back into the partial fractions:

    2x3(x+3)(x2)=95(x+3)+15(x2)\frac{2x - 3}{(x + 3)(x - 2)} = \frac{9}{5(x + 3)} + \frac{1}{5(x - 2)}

Thus, the decomposed form is:

2x3x2+x6=95(x+3)+15(x2)\frac{2x - 3}{x^2 + x - 6} = \frac{9}{5(x + 3)} + \frac{1}{5(x - 2)}

Would you like further details on any step or have additional questions?


Here are some related questions to expand on this topic:

  1. How can we perform partial fraction decomposition when the degree of the numerator is higher than the denominator?
  2. What are the conditions required for partial fraction decomposition?
  3. How do we solve systems of linear equations in general?
  4. Why is it useful to decompose rational expressions?
  5. How can you check the correctness of a decomposition?

Tip: Always double-check the factoring of the denominator, as any mistakes here will affect the entire decomposition.

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Math Problem Analysis

Mathematical Concepts

Algebra
Partial Fraction Decomposition
Factoring Quadratic Expressions

Formulas

Partial fraction decomposition formula

Theorems

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Suitable Grade Level

Grades 10-12