GCEFurther MathematicsPolynomials and Partial Fractions2024

Express $\dfrac{3x^2 + x + 2}{(x^2 + 1)(x - 1)}$ in partial fractions.

A$\dfrac{2x + 1}{x^2 + 1} + \dfrac{3}{x - 1}$
B$\dfrac{x + 2}{x^2 + 1} + \dfrac{3}{x - 1}$
C$\dfrac{2x - 1}{x^2 + 1} + \dfrac{3}{x - 1}$CORRECT
D$\dfrac{x + 1}{x^2 + 1} + \dfrac{2}{x - 1}$
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Why the answer is C, and why the others tempt you.
Let (3x²+x+2)/[(x²+1)(x-1)] = (Ax+B)/(x²+1) + C/(x-1). Multiplying through: 3x²+x+2 = (Ax+B)(x-1) + C(x²+1). Setting x=1: 6 = 2C, so C=3. Expanding and comparing coefficients of x²: A+C=3, so A=0... Comparing constants: -B+C=2, so B=1. Comparing x terms: A-B=1, so A=2. Thus partial fractions = (2x-1)/(x²+1) + 3/(x-1).
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