Let f(x) = (5x² + x + 11) / ((4 + x²)(1 + x))
- (a)Express f(x) in partial fractions.[5]
- (b)Hence show that ∫[0 to 2] f(x) dx = ln 54 – ⅛π.[5]
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2023). The mark or mark type is shown in brackets.
- [B1] State or imply the form (Ax+B)/(4+x²) + C/(1+x)
- [M1] Use a correct method for finding a coefficient
- [A1] Obtain one of A = 2, B = −1 and C = 3
- [A1] Obtain a second value
- [A1] Obtain the third value
- [B1FT] Integrate and obtain terms B/(2) ln(4+x²) + B/2 tan⁻¹(x/2) + C ln(1+x)
- [B1FT] Integral of Ax+B/(4+x²) is A/2 ln(4+x²) + B/2 tan⁻¹(x/2) or (A/2)ln(4 + x²) only. B0FT unless clearly from single term.
- [M1] Substitute limits 0 and 2 correctly in an integral of the form aln(4+x²) + btan⁻¹(x/2) + cln(1+x), where abc≠0
- [A1] AG - work to combine or simplify at least 2 of ln terms is required CWO. A0 if any non exact value(s) seen.
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