Math Problem Statement

Given that \( \frac{2x^2 - 3}{(3 - 2x)(1 - x)^2} \) can be written in the form \( \frac{A}{3 - 2x} + \frac{B}{1 - x} + \frac{C}{(1 - x)^2} \), find the values of A, B, and C.

Solution

The problem asks to express the given rational expression:

2x23(32x)(1x)2\frac{2x^2 - 3}{(3 - 2x)(1 - x)^2}

in the partial fraction form:

A32x+B1x+C(1x)2.\frac{A}{3 - 2x} + \frac{B}{1 - x} + \frac{C}{(1 - x)^2}.


Steps to Solve:

  1. Set up the equation: 2x23(32x)(1x)2=A32x+B1x+C(1x)2.\frac{2x^2 - 3}{(3 - 2x)(1 - x)^2} = \frac{A}{3 - 2x} + \frac{B}{1 - x} + \frac{C}{(1 - x)^2}.

  2. Eliminate the denominators by multiplying through by (32x)(1x)2(3 - 2x)(1 - x)^2: 2x23=A(1x)2+B(32x)(1x)+C(32x).2x^2 - 3 = A(1 - x)^2 + B(3 - 2x)(1 - x) + C(3 - 2x).

  3. Expand each term:

    • Expand A(1x)2A(1 - x)^2: A(1x)2=A(12x+x2)=A(x22x+1).A(1 - x)^2 = A(1 - 2x + x^2) = A(x^2 - 2x + 1).
    • Expand B(32x)(1x)B(3 - 2x)(1 - x): B(32x)(1x)=B(33x2x+2x2)=B(2x25x+3).B(3 - 2x)(1 - x) = B\big(3 - 3x - 2x + 2x^2\big) = B(2x^2 - 5x + 3).
    • Expand C(32x)C(3 - 2x): C(32x)=3C2Cx.C(3 - 2x) = 3C - 2Cx.

    So, the equation becomes: 2x23=A(x22x+1)+B(2x25x+3)+C(32x).2x^2 - 3 = A(x^2 - 2x + 1) + B(2x^2 - 5x + 3) + C(3 - 2x).

  4. Combine like terms: Collect terms involving x2x^2, xx, and the constant terms: 2x23=(A+2B)x2+(2A5B2C)x+(A+3B+3C).2x^2 - 3 = (A + 2B)x^2 + (-2A - 5B - 2C)x + (A + 3B + 3C).

  5. Compare coefficients of x2x^2, xx, and the constant term**: By comparing the left-hand side 2x232x^2 - 3 with the right-hand side, we get:

    • Coefficient of x2x^2: A+2B=2A + 2B = 2,
    • Coefficient of xx: 2A5B2C=0-2A - 5B - 2C = 0,
    • Constant term: A+3B+3C=3A + 3B + 3C = -3.
  6. Solve the system of equations:

    • From A+2B=2A + 2B = 2, we can express A=22BA = 2 - 2B.

    • Substitute A=22BA = 2 - 2B into the other two equations:

      • 2(22B)5B2C=0-2(2 - 2B) - 5B - 2C = 0: 4+4B5B2C=0    4B2C=0    B+2C=4.-4 + 4B - 5B - 2C = 0 \implies -4 - B - 2C = 0 \implies B + 2C = -4.
      • (22B)+3B+3C=3(2 - 2B) + 3B + 3C = -3: 22B+3B+3C=3    2+B+3C=3    B+3C=5.2 - 2B + 3B + 3C = -3 \implies 2 + B + 3C = -3 \implies B + 3C = -5.

      So, we now have a simpler system: B+2C=4,B+3C=5.B + 2C = -4, \quad B + 3C = -5.

    • Subtract the first equation from the second: (B+3C)(B+2C)=5(4)    C=1.(B + 3C) - (B + 2C) = -5 - (-4) \implies C = -1.

    • Substitute C=1C = -1 into B+2C=4B + 2C = -4: B+2(1)=4    B2=4    B=2.B + 2(-1) = -4 \implies B - 2 = -4 \implies B = -2.

    • Substitute B=2B = -2 into A=22BA = 2 - 2B: A=22(2)=2+4=6.A = 2 - 2(-2) = 2 + 4 = 6.

  7. Final Answer: The partial fraction decomposition is: 2x23(32x)(1x)2=632x21x1(1x)2.\frac{2x^2 - 3}{(3 - 2x)(1 - x)^2} = \frac{6}{3 - 2x} - \frac{2}{1 - x} - \frac{1}{(1 - x)^2}.


Let me know if you'd like a detailed explanation of any specific step!


Related Questions:

  1. How do partial fractions simplify solving integrals involving rational expressions?
  2. Could we verify the result by recombining the fractions into a single term?
  3. What happens if the denominator has repeated irreducible quadratic factors instead of linear ones?
  4. How can this decomposition be applied to solve differential equations?
  5. What is the general approach to handling improper fractions before decomposition?

Tip:

When solving for coefficients in partial fractions, systematically organize terms by powers of xx to avoid errors!

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Math Problem Analysis

Mathematical Concepts

Partial Fractions
Algebraic Decomposition
Rational Expressions

Formulas

Partial Fraction Decomposition: \( \frac{P(x)}{Q(x)} = \frac{A}{(ax + b)} + \frac{B}{(cx + d)} + \frac{C}{(ex + f)^2} \)
Solving systems of linear equations to determine coefficients

Theorems

Partial Fraction Decomposition Theorem

Suitable Grade Level

Grades 11-12