AQA C4 2016 June — Question 3 8 marks

Exam BoardAQA
ModuleC4 (Core Mathematics 4)
Year2016
SessionJune
Marks8
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicPolynomial Division & Manipulation
TypeIntegration Using Polynomial Division
DifficultyStandard +0.3 Part (a) is a standard algebraic division exercise requiring polynomial long division or comparison of coefficients—routine C4 content. Part (b) applies the result to integrate term-by-term, yielding a logarithmic answer in the specified form. Both parts follow textbook procedures with no novel insight required, making this slightly easier than average for A-level.
Spec1.02k Simplify rational expressions: factorising, cancelling, algebraic division1.02y Partial fractions: decompose rational functions1.08d Evaluate definite integrals: between limits1.08j Integration using partial fractions

  1. Express \(\frac{3 + 13x - 6x^2}{2x - 3}\) in the form \(Ax + B + \frac{C}{2x - 3}\). [4 marks]
  2. Show that \(\int_3^6 \frac{3 + 13x - 6x^2}{2x - 3} \, dx = p + q \ln 3\), where \(p\) and \(q\) are rational numbers. [4 marks]

Part (a)
AnswerMarks Guidance
\(\frac{3 + 13x - 6x^2}{2x - 3} = Ax + B + \frac{C}{2x - 3}\)M1 e.g. using \(x = \frac{3}{2}\) in an attempt to find \(C\) or forming simultaneous equations and attempt to solve.
\(3 + 13x - 6x^2 = Ax(2x - 3) + B(2x - 3) + C\)
AnswerMarks Guidance
Correct above equation and attempt to find one of \(A\), \(B\) or \(C\) or an attempt at long division
\(A = -3\)A1
\(B = 2\)A1
\(C = 9\)A1 Total: 4
If long division is used award M1 once \(-3x + \cdots\) has been obtained but only award the A marks once the values are clearly identified or it is written in the required form of \(Ax + B + \frac{C}{2x - 3}\)
AnswerMarks
Alternative method of division \(\frac{3+13x-6x^2}{2x-3} = \frac{-3x(2x-3)-9x+13x+3}{2x-3} = -3x + \frac{4x+3}{2x-3}\)M1 for \(-3x + \cdots\),
For the A marks, \(A\), \(B\) and \(C\) must be clearly identified or seen in the required form of \(Ax + B + \frac{C}{2x-3}\)
NMS scores B2 for one correct value, B3 for 2 correct values and B4 for all three correct values
Part (b)
AnswerMarks Guidance
\(\int\frac{3+13x-6x^2}{2x-3}dx = \int(-3x + 2 + \frac{9}{2x-3})dx\)M1
\(= px^2 + qx + r\ln(2x - 3)\)
\(= -\frac{3}{2}x^2 + 2x + \frac{9}{2}\ln(2x - 3)\)A1ft \(\frac{4}{3}x^2 + Bx + \frac{5}{2}\ln(2x - 3)\)
Correct use of \(F(6) - F(3)\)
AnswerMarks Guidance
\(= \left[-\frac{3}{2}\cdot 6^2 + 2.6 + \frac{9}{2}\ln(12 - 3)\right]\)m1 Correct substitution of limits for their \(p, q\) and \(r\).
\(- \left[-\frac{3}{2}\cdot 3^2 + 2.3 + \frac{9}{2}\ln(6 - 3)\right]\)
AnswerMarks Guidance
\(= -\frac{69}{2} + \frac{9}{2}\ln3\)A1 Total: 4
The M1 A1ft and m1 can be earned even if left in terms of \(A, B\) and \(C\) or if 'invented' value(s) for \(A, B\) and \(C\) are used.
Condone missing brackets from the \(\ln(2x - 3)\) term for the M1 mark but only award the A1ft mark if they have clearly recovered; PI by sight of \(\ln9\) or \(\ln3\) after using the limits or a correct final answer.
Treat a decimal answer (should be–29.55 ...) after a correct exact form as ISW but award A0 if an exact answer is not seen.
AnswerMarks Guidance
Total 8
## Part (a)
$\frac{3 + 13x - 6x^2}{2x - 3} = Ax + B + \frac{C}{2x - 3}$ | M1 | e.g. using $x = \frac{3}{2}$ in an attempt to find $C$ or forming simultaneous equations and attempt to solve.

$3 + 13x - 6x^2 = Ax(2x - 3) + B(2x - 3) + C$

Correct above equation and attempt to find one of $A$, $B$ or $C$ or an attempt at long division | |

$A = -3$ | A1 |

$B = 2$ | A1 |

$C = 9$ | A1 | Total: 4

If long division is used award M1 once $-3x + \cdots$ has been obtained but only award the A marks once the values are clearly identified or it is written in the required form of $Ax + B + \frac{C}{2x - 3}$

Alternative method of division $\frac{3+13x-6x^2}{2x-3} = \frac{-3x(2x-3)-9x+13x+3}{2x-3} = -3x + \frac{4x+3}{2x-3}$ | M1 for $-3x + \cdots$,

For the A marks, $A$, $B$ and $C$ must be clearly identified or seen in the required form of $Ax + B + \frac{C}{2x-3}$

NMS scores B2 for one correct value, B3 for 2 correct values and B4 for all three correct values

## Part (b)
$\int\frac{3+13x-6x^2}{2x-3}dx = \int(-3x + 2 + \frac{9}{2x-3})dx$ | M1 |

$= px^2 + qx + r\ln(2x - 3)$ | |

$= -\frac{3}{2}x^2 + 2x + \frac{9}{2}\ln(2x - 3)$ | A1ft | $\frac{4}{3}x^2 + Bx + \frac{5}{2}\ln(2x - 3)$

Correct use of $F(6) - F(3)$

$= \left[-\frac{3}{2}\cdot 6^2 + 2.6 + \frac{9}{2}\ln(12 - 3)\right]$ | m1 | Correct substitution of limits for their $p, q$ and $r$.

$- \left[-\frac{3}{2}\cdot 3^2 + 2.3 + \frac{9}{2}\ln(6 - 3)\right]$

$= -\frac{69}{2} + \frac{9}{2}\ln3$ | A1 | Total: 4 | OE

The M1 A1ft and m1 can be earned even if left in terms of $A, B$ and $C$ or if 'invented' value(s) for $A, B$ and $C$ are used.

Condone missing brackets from the $\ln(2x - 3)$ term for the M1 mark but only award the A1ft mark if they have clearly recovered; PI by sight of $\ln9$ or $\ln3$ after using the limits or a correct final answer.

Treat a decimal answer (should be–29.55 ...) after a correct exact form as ISW but award A0 if an exact answer is not seen.

Total | | 8

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\begin{enumerate}[label=(\alph*)]
\item Express $\frac{3 + 13x - 6x^2}{2x - 3}$ in the form $Ax + B + \frac{C}{2x - 3}$.
[4 marks]

\item Show that $\int_3^6 \frac{3 + 13x - 6x^2}{2x - 3} \, dx = p + q \ln 3$, where $p$ and $q$ are rational numbers.
[4 marks]
\end{enumerate}

\hfill \mbox{\textit{AQA C4 2016 Q3 [8]}}