OCR MEI C1 2015 June — Question 10 12 marks

Exam BoardOCR MEI
ModuleC1 (Core Mathematics 1)
Year2015
SessionJune
Marks12
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicCurve Sketching
TypeVertical translation of cubic with factorisation
DifficultyModerate -0.8 This is a straightforward C1 question testing basic polynomial manipulation and transformations. Part (i) is routine sketching from factored form, (ii) is algebraic expansion, (iii) identifies a simple vertical translation (down 36 units), and (iv) uses factor theorem with polynomial division—all standard textbook exercises requiring no problem-solving insight.
Spec1.03a Straight lines: equation forms y=mx+c, ax+by+c=01.03b Straight lines: parallel and perpendicular relationships1.03d Circles: equation (x-a)^2+(y-b)^2=r^21.03e Complete the square: find centre and radius of circle

10 You are given that \(\mathrm { f } ( x ) = ( x + 3 ) ( x - 2 ) ( x - 5 )\).
  1. Sketch the curve \(y = \mathrm { f } ( x )\).
  2. Show that \(\mathrm { f } ( x )\) may be written as \(x ^ { 3 } - 4 x ^ { 2 } - 11 x + 30\).
  3. Describe fully the transformation that maps the graph of \(y = \mathrm { f } ( x )\) onto the graph of \(y = \mathrm { g } ( x )\), where \(\mathrm { g } ( x ) = x ^ { 3 } - 4 x ^ { 2 } - 11 x - 6\).
  4. Show that \(\mathrm { g } ( - 1 ) = 0\). Hence factorise \(\mathrm { g } ( x )\) completely.

Question 10(i):
AnswerMarks Guidance
AnswerMarks Guidance
Graph of cubic correct way upB1 B0 if stops at \(x\)-axis; must not have any ruled sections; no curving back; condone slight 'flicking out' at ends but not approaching a turning point; allow max on \(y\)-axis or in 1st or 2nd quadrants; condone some 'doubling' or 'feathering'
Crossing \(x\)-axis at \(-3\), \(2\) and \(5\)B1 On graph or nearby; may be in coordinate form; mark intent for intersections with both axes; allow if no graph, but marked on \(x\)-axis; condone intercepts for \(x\) and/or \(y\) given as reversed coordinates
Crossing \(y\)-axis at \(30\)B1 or \(x=0\), \(y=30\) seen if consistent with graph drawn; allow if no graph, but eg B0 for graph with intn on \(y\)-axis nowhere near their indicated 30
Question 10(ii):
AnswerMarks Guidance
AnswerMarks Guidance
Correct expansion of two of the linear factorsM1 May be 3 or 4 terms; condone lack of brackets if correct expansions as if they were there
Correct expansion and completion to given answer \(x^3 - 4x^2 - 11x + 30\)A1 Must be working for this step before given answer; or for direct expansion of all three factors, allow M1 for \(x^3 + 3x^2 - 2x^2 - 5x^2 - 6x - 15x + 10x + 30\), condoning an error in one term, and A1 if no error for completion by stating given answer
Question 10(iii):
AnswerMarks Guidance
AnswerMarks Guidance
TranslationB1 0 for shift or move etc without stating translation; 0 if eg stretch also mentioned
\(\begin{pmatrix} 0 \\ -36 \end{pmatrix}\)B1 or 36 down, or \(-36\) in \(y\) direction oe; if conflict, eg between '\(-36\) in \(y\) direction' and wrong vector, award B0; 0 for '\(-36\) down'
Question 10(iv):
AnswerMarks Guidance
AnswerMarks Guidance
\(-1 - 4 + 11 - 6 = 0\)B1 or B1 for correct division by \((x+1)\) or for the quadratic factor found by inspection, and the conclusion that no remainder means that \(g(-1) = 0\); NB examiners must use annotation in this part; a tick where each mark is earned is sufficient
Attempt at division by \((x+1)\) as far as \(x^3 + x^2\) in workingM1 or inspection with at least two terms of three-term quadratic factor correct; or finding \(f(6) = 0\); M0 for trials of factors to give cubic unless correct answer found with clear correct working, in which case award the M1A1M1A1
Correctly obtaining \(x^2 - 5x - 6\)A1 or \((x-6)\) found as factor
Factorising the correct quadratic factor \(x^2 - 5x - 6\), that has been correctly obtainedM1 For factors giving two terms of quadratic correct or for factors ft one error in quadratic formula or completing square; M0 for formula etc without factors found; for those who have used the factor theorem to find \((x-6)\), M1 for working with cubic to find that \((x+1)\) is repeated; allow for \((x-6)\) and \((x+1)\) given as factors eg after quadratic formula etc
\((x-6)(x+1)^2\) oe iswA1 Condone inclusion of \('=0'\); isw roots found, even if stated as factors; just the answer \((x-6)(x+1)^2\) oe gets last 4 marks
## Question 10(i):
| Answer | Marks | Guidance |
|--------|-------|----------|
| Graph of cubic correct way up | B1 | B0 if stops at $x$-axis; must not have any ruled sections; no curving back; condone slight 'flicking out' at ends but not approaching a turning point; allow max on $y$-axis or in 1st or 2nd quadrants; condone some 'doubling' or 'feathering' |
| Crossing $x$-axis at $-3$, $2$ and $5$ | B1 | On graph or nearby; may be in coordinate form; mark intent for intersections with both axes; allow if no graph, but marked on $x$-axis; condone intercepts for $x$ and/or $y$ given as reversed coordinates |
| Crossing $y$-axis at $30$ | B1 | or $x=0$, $y=30$ seen if consistent with graph drawn; allow if no graph, but eg B0 for graph with intn on $y$-axis nowhere near their indicated 30 |

## Question 10(ii):
| Answer | Marks | Guidance |
|--------|-------|----------|
| Correct expansion of two of the linear factors | M1 | May be 3 or 4 terms; condone lack of brackets if correct expansions as if they were there |
| Correct expansion and completion to given answer $x^3 - 4x^2 - 11x + 30$ | A1 | Must be working for this step before given answer; or for direct expansion of all three factors, allow M1 for $x^3 + 3x^2 - 2x^2 - 5x^2 - 6x - 15x + 10x + 30$, condoning an error in one term, and A1 if no error for completion by stating given answer |

## Question 10(iii):
| Answer | Marks | Guidance |
|--------|-------|----------|
| Translation | B1 | 0 for shift or move etc without stating translation; 0 if eg stretch also mentioned |
| $\begin{pmatrix} 0 \\ -36 \end{pmatrix}$ | B1 | or 36 down, or $-36$ in $y$ direction oe; if conflict, eg between '$-36$ in $y$ direction' and wrong vector, award B0; 0 for '$-36$ down' |

## Question 10(iv):
| Answer | Marks | Guidance |
|--------|-------|----------|
| $-1 - 4 + 11 - 6 = 0$ | B1 | or B1 for correct division by $(x+1)$ or for the quadratic factor found by inspection, and the conclusion that no remainder means that $g(-1) = 0$; NB examiners must use annotation in this part; a tick where each mark is earned is sufficient |
| Attempt at division by $(x+1)$ as far as $x^3 + x^2$ in working | M1 | or inspection with at least two terms of three-term quadratic factor correct; or finding $f(6) = 0$; M0 for trials of factors to give cubic unless correct answer found with clear correct working, in which case award the M1A1M1A1 |
| Correctly obtaining $x^2 - 5x - 6$ | A1 | or $(x-6)$ found as factor |
| Factorising the correct quadratic factor $x^2 - 5x - 6$, that has been correctly obtained | M1 | For factors giving two terms of quadratic correct or for factors ft one error in quadratic formula or completing square; M0 for formula etc without factors found; for those who have used the factor theorem to find $(x-6)$, M1 for working with cubic to find that $(x+1)$ is repeated; allow for $(x-6)$ and $(x+1)$ given as factors eg after quadratic formula etc |
| $(x-6)(x+1)^2$ oe isw | A1 | Condone inclusion of $'=0'$; isw roots found, even if stated as factors; just the answer $(x-6)(x+1)^2$ oe gets last 4 marks |
10 You are given that $\mathrm { f } ( x ) = ( x + 3 ) ( x - 2 ) ( x - 5 )$.\\
(i) Sketch the curve $y = \mathrm { f } ( x )$.\\
(ii) Show that $\mathrm { f } ( x )$ may be written as $x ^ { 3 } - 4 x ^ { 2 } - 11 x + 30$.\\
(iii) Describe fully the transformation that maps the graph of $y = \mathrm { f } ( x )$ onto the graph of $y = \mathrm { g } ( x )$, where $\mathrm { g } ( x ) = x ^ { 3 } - 4 x ^ { 2 } - 11 x - 6$.\\
(iv) Show that $\mathrm { g } ( - 1 ) = 0$. Hence factorise $\mathrm { g } ( x )$ completely.

\hfill \mbox{\textit{OCR MEI C1 2015 Q10 [12]}}