Algebra · real student question

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

Question

Write

x(x2)2\frac{x}{(x-2)^2}

as a sum of partial fractions.

Step-by-step solution

  1. Rewrite the numerator in terms of the denominator's base. The denominator is built from x2x-2, so express xx using that same block:

    x=(x2)+2x=(x-2)+2

    This is an identity, so nothing has been assumed — it simply reorganises the numerator.

  2. Substitute and split the single fraction into two.

    x(x2)2=(x2)+2(x2)2=x2(x2)2+2(x2)2\frac{x}{(x-2)^2}=\frac{(x-2)+2}{(x-2)^2}=\frac{x-2}{(x-2)^2}+\frac{2}{(x-2)^2}

  3. Cancel in the first fraction. One factor of (x2)(x-2) divides out:

    x2(x2)2=1x2\frac{x-2}{(x-2)^2}=\frac{1}{x-2}

    x(x2)2=1x2+2(x2)2,x2\frac{x}{(x-2)^2}=\frac{1}{x-2}+\frac{2}{(x-2)^2},\qquad x\neq 2

  4. Compare with the algebraic method. Setting x(x2)2=Ax2+B(x2)2\tfrac{x}{(x-2)^2}=\tfrac{A}{x-2}+\tfrac{B}{(x-2)^2} gives x=A(x2)+Bx=A(x-2)+B, so A=1A=1 and B=2B=2 — the same answer. The numerator trick reaches it in one line and is worth recognising whenever the numerator is linear and the denominator is a repeated linear factor.

  5. Check numerically. At x=4x=4: left =44=1=\tfrac44=1, right =12+24=1=\tfrac12+\tfrac24=1 \checkmark. At x=0x=0: left =0=0, right =12+24=0=-\tfrac12+\tfrac24=0 \checkmark.

Answer

x(x2)2=1x2+2(x2)2,x2\frac{x}{(x-2)^2}=\frac{1}{x-2}+\frac{2}{(x-2)^2},\qquad x\neq 2

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