Algebra · real student question

Decompose (2x - 1)/(x - 1)^2 into partial fractions.

Question

Decompose

2x1(x1)2\frac{2x-1}{(x-1)^2}

into partial fractions.

Step-by-step solution

  1. Pick the template that a repeated factor demands. The denominator is the single linear factor (x1)(x-1) raised to the power 22, so the decomposition needs a term for every power from 11 up to 22:

    2x1(x1)2=Ax1+B(x1)2\frac{2x-1}{(x-1)^2}=\frac{A}{x-1}+\frac{B}{(x-1)^2}

    Using only the (x1)2(x-1)^2 term leaves one unknown for a degree-1 numerator, which cannot work in general.

  2. Clear the denominators. Multiplying both sides by (x1)2(x-1)^2:

    2x1=A(x1)+B2x-1=A(x-1)+B

  3. Expand and collect by powers of xx.

    2x1=Ax+(BA)2x-1=Ax+(B-A)

  4. Equate coefficients. Matching the xx terms gives A=2A=2; matching the constants gives BA=1B-A=-1, so

    B=A1=1B=A-1=1

  5. Cross-check with a shortcut substitution. Putting x=1x=1 into 2x1=A(x1)+B2x-1=A(x-1)+B kills the AA term immediately and gives B=2(1)1=1B=2(1)-1=1 ✓ - a useful independent confirmation of the coefficient method.

  6. State the result and verify numerically.

    2x1(x1)2=2x1+1(x1)2,x1\frac{2x-1}{(x-1)^2}=\frac{2}{x-1}+\frac{1}{(x-1)^2},\qquad x\neq 1

    At x=3x=3: left =frac54=1.25= frac{5}{4}=1.25, right =frac22+frac14=1.25= frac{2}{2}+ frac{1}{4}=1.25 ✓. At x=0.5x=0.5: left =0=0, right =4+4=0=-4+4=0 ✓.

Answer

2x1(x1)2=2x1+1(x1)2,x1\frac{2x-1}{(x-1)^2}=\frac{2}{x-1}+\frac{1}{(x-1)^2},\qquad x\neq 1

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