OCR FP2 2012 June — Question 8 12 marks

Exam BoardOCR
ModuleFP2 (Further Pure Mathematics 2)
Year2012
SessionJune
Marks12
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicConic sections
TypeConic translation and transformation
DifficultyChallenging +1.2 This is a multi-step Further Maths question requiring systematic application of asymptote properties, algebraic manipulation, and curve analysis. While it involves several techniques (finding rational functions from asymptotes, range finding, intersection conditions), each step follows standard FP2 methods without requiring novel insight. The structure is scaffolded and the techniques are well-practiced in Further Maths syllabi, making it moderately above average difficulty but not exceptionally challenging.
Spec1.02n Sketch curves: simple equations including polynomials1.02q Use intersection points: of graphs to solve equations1.02y Partial fractions: decompose rational functions

8 The curve \(C _ { 1 }\) has equation \(y = \frac { \mathrm { p } ( x ) } { \mathrm { q } ( x ) }\), where \(\mathrm { p } ( x )\) and \(\mathrm { q } ( x )\) are polynomials of degree 2 and 1 respectively. The asymptotes of the curve are \(x = - 2\) and \(y = \frac { 1 } { 2 } x + 1\), and the curve passes through the point \(\left( - 1 , \frac { 17 } { 2 } \right)\).
  1. Express the equation of \(C _ { 1 }\) in the form \(y = \frac { \mathrm { p } ( x ) } { \mathrm { q } ( x ) }\).
  2. For the curve \(C _ { 1 }\), find the range of values that \(y\) can take.
  3. For the curve \(C _ { 1 }\), find the range of values that \(y\) can take.
    Another curve, \(C _ { 2 }\), has equation \(y ^ { 2 } = \frac { \mathrm { p } ( x ) } { \mathrm { q } ( x ) }\), where \(\mathrm { p } ( x )\) and \(\mathrm { q } ( x )\) are the polynomials found in part (i).
  4. It is given that \(C _ { 2 }\) intersects the line \(y = \frac { 1 } { 2 } x + 1\) exactly once. Find the coordinates of the point of intersection. Another curve, \(C _ { 2 }\), has equation \(y ^ { 2 } = \frac { \mathrm { p } ( x ) } { \mathrm { q } ( x ) }\), where \(\mathrm { p } ( x )\) and \(\mathrm { q } ( x )\) are the polynomials found in part (i).
  5. It is given that \(C _ { 2 }\) intersects the line \(y = \frac { 1 } { 2 } x + 1\) exactly once. Find the coordinates of the point of
    intersection. \section*{THERE ARE NO QUESTIONS WRITTEN ON THIS PAGE.}

Question 8:
Part (i):
AnswerMarks Guidance
AnswerMarks Guidance
\(q(x) = x+2\)B1 For correct \(q(x)\) soi oe
\(y = \dfrac{A}{x+2} + \frac{1}{2}x + 1\)M1 For expressing \(y\) in this form. Allow \(cx+d\) for \(A\)
\(\left(-1, \frac{17}{2}\right) \Rightarrow A = 8\)A1 For correct \(A\)
\(y = \dfrac{\frac{1}{2}x^2 + 2x + 10}{x+2} \Rightarrow p(x) = \tfrac{1}{2}x^2 + 2x + 10\)A1 For correct \(p(x)\). Allow equal multiples of \(p(x)\) and \(q(x)\)
[4]
Alternative:
AnswerMarks Guidance
AnswerMarks Guidance
\(q(x) = x+2\)B1 For correct \(q(x)\) soi oe
\(y = \dfrac{ax^2+bx+c}{q(x)} = ax + (b-2a) + \dfrac{c-2b+4a}{x+2}\)M1 For division by their \(q(x)\); 1st line of division and 1st term in quotient should be seen for correct method
\(y = \frac{1}{2}x+1 \Rightarrow a=\frac{1}{2},\ b=2\)A1 For correct \(a\) and \(b\) oe
\(\left(-1,\frac{17}{2}\right) \Rightarrow c-2b+4a = 8 \Rightarrow c=10\)A1 For correct \(c\) oe
Part (ii):
AnswerMarks Guidance
AnswerMarks Guidance
\(\frac{1}{2}x^2 + (2-y)x + 10 - 2y = 0\)M1 For attempt to rearrange as quadratic in \(x\)
\(b^2 - 4ac \geq 0 \Rightarrow (2-y)^2 \geq 2(10-2y)\)M1 For use of \(b^2-4ac\) (\(\leq\) or \(\geq\) or \(=\) or \(<\) or \(>\))
\(\Rightarrow y^2 \geq 16 \Rightarrow \{y \leq -4,\ y \geq 4\}\)A1 For critical values \(\pm 4\)
*(pto for alternative)*A1 For correct range. (Must be \(\leq\) and \(\geq\)) www
[4]
Alternative to 8(ii):
AnswerMarks Guidance
AnswerMarks Guidance
\(\dfrac{dy}{dx} = \dfrac{(x+2)(x+2) - \left(\frac{1}{2}x^2+2x+10\right)}{(x+2)^2}\)M1 Differentiation using quotient rule
\(= 0\) when \((x+2)^2 = \frac{1}{2}x^2+2x+10\)M1 Attempt to find solution using \(\frac{dy}{dx}=0\)
\(\Rightarrow \frac{1}{2}x^2+2x-6=0 \Rightarrow x^2+4x-12=0\)
\(\Rightarrow (x+6)(x-2)=0\)
\(\Rightarrow x=2,\ y=4 \quad x=-6,\ y=-4\)A1
\(\{y \leq -4,\ y \geq 4\}\)A1 For correct range. (Must be \(\leq\) and \(\geq\)) www
Alternatively:
AnswerMarks Guidance
AnswerMarks Guidance
\(y = \frac{1}{2}x+1+\dfrac{8}{x+2}\)
\(\Rightarrow \dfrac{dy}{dx} = \frac{1}{2} - \dfrac{8}{(x+2)^2}\)M1 Differentiation using chain rule
\(= 0\) when \(\frac{1}{2} - \dfrac{8}{(x+2)^2} \Rightarrow (x+2)^2 = 16\)M1 Attempt to find solution using \(\frac{dy}{dx}=0\)
\(\Rightarrow x+2=\pm4 \Rightarrow x=2\) or \(-6\)
\(\Rightarrow y=4\) or \(-4\)A1 For correct range. (Must be \(\leq\) and \(\geq\)) www
\(\{y \leq -4,\ y \geq 4\}\)A1
Part (iii):
AnswerMarks Guidance
AnswerMarks Guidance
\(\left(\frac{1}{2}x+1\right)^2 = \dfrac{\frac{1}{2}x^2+2x+10}{x+2}\) OR \(y^2 = \dfrac{4}{y}+y\)B1ft For a correct equation derived from intersection of \(C_2\) with \(y=\frac{1}{2}x+1\) FT from (i)
\(\Rightarrow x^3+4x^2+4x-32=0\) OR \(y^3-y^2-4=0\)M1 For obtaining a cubic
A1Correct cubic
\(\Rightarrow (2,\ 2)\)A1 Coordinates correct www
[4]
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## Question 8:

### Part (i):

| Answer | Marks | Guidance |
|--------|-------|----------|
| $q(x) = x+2$ | B1 | For correct $q(x)$ **soi oe** |
| $y = \dfrac{A}{x+2} + \frac{1}{2}x + 1$ | M1 | For expressing $y$ in this form. Allow $cx+d$ for $A$ |
| $\left(-1, \frac{17}{2}\right) \Rightarrow A = 8$ | A1 | For correct $A$ |
| $y = \dfrac{\frac{1}{2}x^2 + 2x + 10}{x+2} \Rightarrow p(x) = \tfrac{1}{2}x^2 + 2x + 10$ | A1 | For correct $p(x)$. Allow equal multiples of $p(x)$ and $q(x)$ |

**[4]**

**Alternative:**

| Answer | Marks | Guidance |
|--------|-------|----------|
| $q(x) = x+2$ | B1 | For correct $q(x)$ **soi oe** |
| $y = \dfrac{ax^2+bx+c}{q(x)} = ax + (b-2a) + \dfrac{c-2b+4a}{x+2}$ | M1 | For division by their $q(x)$; 1st line of division and 1st term in quotient should be seen for correct method |
| $y = \frac{1}{2}x+1 \Rightarrow a=\frac{1}{2},\ b=2$ | A1 | For correct $a$ and $b$ **oe** |
| $\left(-1,\frac{17}{2}\right) \Rightarrow c-2b+4a = 8 \Rightarrow c=10$ | A1 | For correct $c$ **oe** |

### Part (ii):

| Answer | Marks | Guidance |
|--------|-------|----------|
| $\frac{1}{2}x^2 + (2-y)x + 10 - 2y = 0$ | M1 | For attempt to rearrange as quadratic in $x$ |
| $b^2 - 4ac \geq 0 \Rightarrow (2-y)^2 \geq 2(10-2y)$ | M1 | For use of $b^2-4ac$ ($\leq$ or $\geq$ or $=$ or $<$ or $>$) |
| $\Rightarrow y^2 \geq 16 \Rightarrow \{y \leq -4,\ y \geq 4\}$ | A1 | For critical values $\pm 4$ |
| *(pto for alternative)* | A1 | For correct range. (Must be $\leq$ and $\geq$) **www** |

**[4]**

**Alternative to 8(ii):**

| Answer | Marks | Guidance |
|--------|-------|----------|
| $\dfrac{dy}{dx} = \dfrac{(x+2)(x+2) - \left(\frac{1}{2}x^2+2x+10\right)}{(x+2)^2}$ | M1 | Differentiation using quotient rule |
| $= 0$ when $(x+2)^2 = \frac{1}{2}x^2+2x+10$ | M1 | Attempt to find solution using $\frac{dy}{dx}=0$ |
| $\Rightarrow \frac{1}{2}x^2+2x-6=0 \Rightarrow x^2+4x-12=0$ | | |
| $\Rightarrow (x+6)(x-2)=0$ | | |
| $\Rightarrow x=2,\ y=4 \quad x=-6,\ y=-4$ | A1 | |
| $\{y \leq -4,\ y \geq 4\}$ | A1 | For correct range. (Must be $\leq$ and $\geq$) **www** |

**Alternatively:**

| Answer | Marks | Guidance |
|--------|-------|----------|
| $y = \frac{1}{2}x+1+\dfrac{8}{x+2}$ | | |
| $\Rightarrow \dfrac{dy}{dx} = \frac{1}{2} - \dfrac{8}{(x+2)^2}$ | M1 | Differentiation using chain rule |
| $= 0$ when $\frac{1}{2} - \dfrac{8}{(x+2)^2} \Rightarrow (x+2)^2 = 16$ | M1 | Attempt to find solution using $\frac{dy}{dx}=0$ |
| $\Rightarrow x+2=\pm4 \Rightarrow x=2$ or $-6$ | | |
| $\Rightarrow y=4$ or $-4$ | A1 | For correct range. (Must be $\leq$ and $\geq$) **www** |
| $\{y \leq -4,\ y \geq 4\}$ | A1 | |

### Part (iii):

| Answer | Marks | Guidance |
|--------|-------|----------|
| $\left(\frac{1}{2}x+1\right)^2 = \dfrac{\frac{1}{2}x^2+2x+10}{x+2}$ **OR** $y^2 = \dfrac{4}{y}+y$ | B1ft | For a correct equation derived from intersection of $C_2$ with $y=\frac{1}{2}x+1$ FT from (i) |
| $\Rightarrow x^3+4x^2+4x-32=0$ **OR** $y^3-y^2-4=0$ | M1 | For obtaining a cubic |
| | A1 | Correct cubic |
| $\Rightarrow (2,\ 2)$ | A1 | Coordinates correct **www** |

**[4]**

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8 The curve $C _ { 1 }$ has equation $y = \frac { \mathrm { p } ( x ) } { \mathrm { q } ( x ) }$, where $\mathrm { p } ( x )$ and $\mathrm { q } ( x )$ are polynomials of degree 2 and 1 respectively. The asymptotes of the curve are $x = - 2$ and $y = \frac { 1 } { 2 } x + 1$, and the curve passes through the point $\left( - 1 , \frac { 17 } { 2 } \right)$.\\
(i) Express the equation of $C _ { 1 }$ in the form $y = \frac { \mathrm { p } ( x ) } { \mathrm { q } ( x ) }$.\\
(ii) For the curve $C _ { 1 }$, find the range of values that $y$ can take.\\
(ii) For the curve $C _ { 1 }$, find the range of values that $y$ can take.\\
Another curve, $C _ { 2 }$, has equation $y ^ { 2 } = \frac { \mathrm { p } ( x ) } { \mathrm { q } ( x ) }$, where $\mathrm { p } ( x )$ and $\mathrm { q } ( x )$ are the polynomials found in part (i).\\
(iii) It is given that $C _ { 2 }$ intersects the line $y = \frac { 1 } { 2 } x + 1$ exactly once. Find the coordinates of the point of intersection.

Another curve, $C _ { 2 }$, has equation $y ^ { 2 } = \frac { \mathrm { p } ( x ) } { \mathrm { q } ( x ) }$, where $\mathrm { p } ( x )$ and $\mathrm { q } ( x )$ are the polynomials found in part (i).\\
(iii) It is given that $C _ { 2 }$ intersects the line $y = \frac { 1 } { 2 } x + 1$ exactly once. Find the coordinates of the point of\\
intersection.

\section*{THERE ARE NO QUESTIONS WRITTEN ON THIS PAGE.}

\hfill \mbox{\textit{OCR FP2 2012 Q8 [12]}}