Question:

If \[ \frac{3x-1}{(x-1)(x-2)(x-3)} = \frac{A}{x-1} + \frac{B}{x-2} + \frac{C}{x-3}, \] then the values of \((A,B,C)\) are

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For partial fractions with linear factors, substitute the roots of the denominator factors to find constants quickly.
  • \((1,-5,4)\)
  • \((1,5,4)\)
  • \((4,5,1)\)
  • \((1,4,5)\)
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The Correct Option is A

Solution and Explanation

We are given \[ \frac{3x-1}{(x-1)(x-2)(x-3)} = \frac{A}{x-1}+\frac{B}{x-2}+\frac{C}{x-3}. \] Multiplying both sides by \((x-1)(x-2)(x-3)\), we get \[ 3x-1=A(x-2)(x-3)+B(x-1)(x-3)+C(x-1)(x-2). \] Now use suitable values of \(x\) to find \(A\), \(B\), and \(C\). Put \[ x=1. \] Then, \[ 3(1)-1=A(1-2)(1-3). \] \[ 2=A(-1)(-2). \] \[ 2=2A. \] \[ A=1. \] Now put \[ x=2. \] Then, \[ 3(2)-1=B(2-1)(2-3). \] \[ 6-1=B(1)(-1). \] \[ 5=-B. \] \[ B=-5. \] Now put \[ x=3. \] Then, \[ 3(3)-1=C(3-1)(3-2). \] \[ 9-1=C(2)(1). \] \[ 8=2C. \] \[ C=4. \] Therefore, \[ (A,B,C)=(1,-5,4). \]
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