Edexcel C12 2017 January — Question 6 11 marks

Exam BoardEdexcel
ModuleC12 (Core Mathematics 1 & 2)
Year2017
SessionJanuary
Marks11
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicStraight Lines & Coordinate Geometry
TypePerpendicular line through point
DifficultyModerate -0.8 This is a straightforward multi-part question testing basic coordinate geometry: finding gradient from an equation, x-intercept, perpendicular gradient, equation of a line, and triangle area. All steps are routine applications of standard formulas with no problem-solving insight required. Easier than average A-level questions.
Spec1.03a Straight lines: equation forms y=mx+c, ax+by+c=01.03b Straight lines: parallel and perpendicular relationships

6. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{f39ade34-32e2-4b5c-b80a-9663c6a65c87-08_906_1100_127_388} \captionsetup{labelformat=empty} \caption{Figure 2}
\end{figure} The straight line \(l _ { 1 }\) has equation \(2 y = 3 x + 5\) The line \(l _ { 1 }\) cuts the \(x\)-axis at the point \(A\), as shown in Figure 2.
    1. State the gradient of \(l _ { 1 }\)
    2. Write down the \(x\) coordinate of point \(A\). Another straight line \(l _ { 2 }\) intersects \(l _ { 1 }\) at the point \(B\) with \(x\) coordinate 1 and crosses the \(x\)-axis at the point \(C\), as shown in Figure 2. Given that \(l _ { 2 }\) is perpendicular to \(l _ { 1 }\)
  1. find an equation for \(l _ { 2 }\) in the form \(a x + b y + c = 0\), where \(a\), b and \(c\) are integers,
  2. find the exact area of triangle \(A B C\).

Question 6(a)(i):
AnswerMarks Guidance
Answer/WorkingMark Guidance
\(\frac{3}{2}\)B1 Accept exact equivalents
Question 6(a)(ii):
AnswerMarks Guidance
Answer/WorkingMark Guidance
\(y = 0, \quad 3x + 5 = 0 \Rightarrow x = -\frac{5}{3}\)M1A1 M1: Sets \(y = 0\) and attempts to find \(x\). Accept as evidence \(3x+5=0 \Rightarrow x=..\) or awrt \(-1.7\). A1: \(x = -\frac{5}{3}\) or exact equivalent including \(1.\dot{6}\) (i.e. a clear dot over the 6)
Question 6(b):
AnswerMarks Guidance
Answer/WorkingMark Guidance
Gradient \(l_2 = -\frac{1}{\frac{3}{2}} = -\frac{2}{3}\)M1 Uses \(m_2 = -\frac{1}{m_1}\) to find the gradient of \(l_2\) (may be implied by their line equation). Allow an attempt to find \(m_2\) from \(m_1 \times m_2 = -1\)
Point \(B\) has \(y\) coordinate of 4B1 This may be embedded within the equation of the line but must be seen in part (b).
e.g. \(y - \text{'4'} = -\frac{2}{3}(x-1)\) or \(\frac{y-\text{'4'}}{x-1} = -\frac{2}{3}\)M1 A correct straight line method with a changed gradient and their point \((1, \text{'4'})\). There must have been attempt to find the \(y\) coordinate of \(B\). If using \(y = mx + c\), must reach as far as finding a value for \(c\).
e.g. \(y - 4 = -\frac{2}{3}(x-1)\) or \(\frac{y-4}{x-1} = -\frac{2}{3}\)A1 A correct un-simplified equation
\(2x + 3y - 14 = 0\)A1 Accept \(A(2x+3y-14)=0\) where \(A\) is an integer. Terms can be in any order but must have '\(= 0\)'.
Question 6(b) Alt:
AnswerMarks Guidance
Answer/WorkingMark Guidance
Gradient \(l_2 = -\frac{1}{\frac{3}{2}} = -\frac{2}{3}\)M1 Uses \(m_2 = -\frac{1}{m_1}\) to find the gradient of \(l_2\) as before
\(\frac{3}{2}x + \frac{5}{2} = -\frac{2}{3}x + c\)B1 A correct statement for \(l_1 = l_2\)
\(x = 1 \Rightarrow c = \frac{14}{3}\)M1 Substitutes \(x = 1\) to find a value for \(c\)
\(y = -\frac{2}{3}x + \frac{14}{3}\)A1 Correct equation
\(2x + 3y - 14 = 0\)A1 Accept \(A(2x+3y-14)=0\) where \(A\) is an integer.
Question 6(c):
AnswerMarks Guidance
Answer/WorkingMark Guidance
\(y = 0 \Rightarrow 2x - 14 = 0 \Rightarrow x = 7\)M1 Attempts to find \(C\) using \(y = 0\) in the equation obtained in part (b)
\(= \frac{1}{2} \times \left(\text{'7'} + \text{'}\frac{5}{3}\text{'}\right) \times \text{'4'}\)M1 Attempts area of triangle using \(\frac{1}{2} \times AC \times (y \text{ coord of } B)\)
\(= \frac{52}{3}\)A1 Area \(= \frac{52}{3}\) or exact equivalent e.g. \(17\frac{1}{3}\) or \(17.\dot{3}\) (i.e. a clear dot over the 3)
Question 6(c) Way 2:
AnswerMarks Guidance
Answer/WorkingMark Guidance
\(y = 0 \Rightarrow 2x - 14 = 0 \Rightarrow x = 7\)M1 Attempts to find \(C\) using \(y = 0\) in the equation obtained in part (b)
\(\frac{1}{2}AB \times BC = \frac{1}{2}\sqrt{\frac{208}{9}} \times \sqrt{52}\)M1 A complete method for the area including correct attempts at finding \(AB\) and \(BC\) using their values.
\(= \frac{52}{3}\)A1 Area \(= \frac{52}{3}\) or exact equivalent e.g. \(17\frac{1}{3}\) or \(17.\dot{3}\) (i.e. a clear dot over the 3)
Question 6(c) Way 3:
AnswerMarks Guidance
Answer/WorkingMark Guidance
\(y = 0 \Rightarrow 2x - 14 = 0 \Rightarrow x = 7\)M1 Attempts to find \(C\) using \(y = 0\) in the equation obtained in part (b)
\(\frac{1}{2}\begin{vmatrix} 1 & 7 & -\frac{5}{3} & 1 \\ 4 & 0 & 0 & 4 \end{vmatrix} = \frac{1}{2}\left\vert -\frac{20}{3} - 28\right\vert\)M1 Uses shoelace method. Must see a correct method including \(\frac{1}{2}\).
\(= \frac{52}{3}\)A1 Area \(= \frac{52}{3}\) or exact equivalent e.g. \(17\frac{1}{3}\) or \(17.\dot{3}\) (i.e. a clear dot over the 3)
Question 6(c) Way 4:
AnswerMarks Guidance
Answer/WorkingMark Guidance
\(y = 0 \Rightarrow 2x - 14 = 0 \Rightarrow x = 7\)M1 Attempts to find \(C\) using \(y = 0\) in the equation obtained in part (b)
\(\int_{-\frac{5}{3}}^{1}\left(\frac{3x}{2}+\frac{5}{2}\right)dx + \int_{1}^{7}\left(-\frac{2x}{3}+\frac{14}{3}\right)dx = \left[\frac{3x^2}{4}+\frac{5}{2}x\right]_{-\frac{5}{3}}^{1} + \left[-\frac{2x^2}{6}+\frac{14}{3}x\right]_{1}^{7}\)M1 A complete method using their values with correct integration on \(l_1\) and their \(l_2\)
\(= \frac{52}{3}\)A1 Area \(= \frac{52}{3}\) or exact equivalent e.g. \(17\frac{1}{3}\) or \(17.\dot{3}\) (i.e. a clear dot over the 3)
# Question 6(a)(i):

| Answer/Working | Mark | Guidance |
|---|---|---|
| $\frac{3}{2}$ | B1 | Accept exact equivalents |

# Question 6(a)(ii):

| Answer/Working | Mark | Guidance |
|---|---|---|
| $y = 0, \quad 3x + 5 = 0 \Rightarrow x = -\frac{5}{3}$ | M1A1 | M1: Sets $y = 0$ and attempts to find $x$. Accept as evidence $3x+5=0 \Rightarrow x=..$ or awrt $-1.7$. A1: $x = -\frac{5}{3}$ or exact equivalent including $1.\dot{6}$ **(i.e. a clear dot over the 6)** |

# Question 6(b):

| Answer/Working | Mark | Guidance |
|---|---|---|
| Gradient $l_2 = -\frac{1}{\frac{3}{2}} = -\frac{2}{3}$ | M1 | Uses $m_2 = -\frac{1}{m_1}$ to find the gradient of $l_2$ (may be implied by their line equation). Allow an attempt to find $m_2$ from $m_1 \times m_2 = -1$ |
| Point $B$ has $y$ coordinate of 4 | B1 | This may be embedded within the equation of the line but must be seen in part (b). |
| e.g. $y - \text{'4'} = -\frac{2}{3}(x-1)$ or $\frac{y-\text{'4'}}{x-1} = -\frac{2}{3}$ | M1 | A correct straight line method with a changed gradient and their point $(1, \text{'4'})$. There must have been attempt to find the $y$ coordinate of $B$. If using $y = mx + c$, must reach as far as finding a value for $c$. |
| e.g. $y - 4 = -\frac{2}{3}(x-1)$ or $\frac{y-4}{x-1} = -\frac{2}{3}$ | A1 | A correct un-simplified equation |
| $2x + 3y - 14 = 0$ | A1 | Accept $A(2x+3y-14)=0$ where $A$ is an integer. Terms can be in any order but must have '$= 0$'. |

# Question 6(b) Alt:

| Answer/Working | Mark | Guidance |
|---|---|---|
| Gradient $l_2 = -\frac{1}{\frac{3}{2}} = -\frac{2}{3}$ | M1 | Uses $m_2 = -\frac{1}{m_1}$ to find the gradient of $l_2$ as before |
| $\frac{3}{2}x + \frac{5}{2} = -\frac{2}{3}x + c$ | B1 | A correct statement for $l_1 = l_2$ |
| $x = 1 \Rightarrow c = \frac{14}{3}$ | M1 | Substitutes $x = 1$ to find a value for $c$ |
| $y = -\frac{2}{3}x + \frac{14}{3}$ | A1 | Correct equation |
| $2x + 3y - 14 = 0$ | A1 | Accept $A(2x+3y-14)=0$ where $A$ is an integer. |

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# Question 6(c):

| Answer/Working | Mark | Guidance |
|---|---|---|
| $y = 0 \Rightarrow 2x - 14 = 0 \Rightarrow x = 7$ | M1 | Attempts to find $C$ using $y = 0$ in the equation obtained in part (b) |
| $= \frac{1}{2} \times \left(\text{'7'} + \text{'}\frac{5}{3}\text{'}\right) \times \text{'4'}$ | M1 | Attempts area of triangle using $\frac{1}{2} \times AC \times (y \text{ coord of } B)$ |
| $= \frac{52}{3}$ | A1 | Area $= \frac{52}{3}$ or exact equivalent e.g. $17\frac{1}{3}$ or $17.\dot{3}$ **(i.e. a clear dot over the 3)** |

# Question 6(c) Way 2:

| Answer/Working | Mark | Guidance |
|---|---|---|
| $y = 0 \Rightarrow 2x - 14 = 0 \Rightarrow x = 7$ | M1 | Attempts to find $C$ using $y = 0$ in the equation obtained in part (b) |
| $\frac{1}{2}AB \times BC = \frac{1}{2}\sqrt{\frac{208}{9}} \times \sqrt{52}$ | M1 | A complete method for the area including correct attempts at finding $AB$ and $BC$ using their values. |
| $= \frac{52}{3}$ | A1 | Area $= \frac{52}{3}$ or exact equivalent e.g. $17\frac{1}{3}$ or $17.\dot{3}$ **(i.e. a clear dot over the 3)** |

# Question 6(c) Way 3:

| Answer/Working | Mark | Guidance |
|---|---|---|
| $y = 0 \Rightarrow 2x - 14 = 0 \Rightarrow x = 7$ | M1 | Attempts to find $C$ using $y = 0$ in the equation obtained in part (b) |
| $\frac{1}{2}\begin{vmatrix} 1 & 7 & -\frac{5}{3} & 1 \\ 4 & 0 & 0 & 4 \end{vmatrix} = \frac{1}{2}\left\vert -\frac{20}{3} - 28\right\vert$ | M1 | Uses shoelace method. Must see a correct method including $\frac{1}{2}$. |
| $= \frac{52}{3}$ | A1 | Area $= \frac{52}{3}$ or exact equivalent e.g. $17\frac{1}{3}$ or $17.\dot{3}$ **(i.e. a clear dot over the 3)** |

# Question 6(c) Way 4:

| Answer/Working | Mark | Guidance |
|---|---|---|
| $y = 0 \Rightarrow 2x - 14 = 0 \Rightarrow x = 7$ | M1 | Attempts to find $C$ using $y = 0$ in the equation obtained in part (b) |
| $\int_{-\frac{5}{3}}^{1}\left(\frac{3x}{2}+\frac{5}{2}\right)dx + \int_{1}^{7}\left(-\frac{2x}{3}+\frac{14}{3}\right)dx = \left[\frac{3x^2}{4}+\frac{5}{2}x\right]_{-\frac{5}{3}}^{1} + \left[-\frac{2x^2}{6}+\frac{14}{3}x\right]_{1}^{7}$ | M1 | A complete method using their values with correct integration on $l_1$ and their $l_2$ |
| $= \frac{52}{3}$ | A1 | Area $= \frac{52}{3}$ or exact equivalent e.g. $17\frac{1}{3}$ or $17.\dot{3}$ **(i.e. a clear dot over the 3)** |

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6.

\begin{figure}[h]
\begin{center}
  \includegraphics[alt={},max width=\textwidth]{f39ade34-32e2-4b5c-b80a-9663c6a65c87-08_906_1100_127_388}
\captionsetup{labelformat=empty}
\caption{Figure 2}
\end{center}
\end{figure}

The straight line $l _ { 1 }$ has equation $2 y = 3 x + 5$\\
The line $l _ { 1 }$ cuts the $x$-axis at the point $A$, as shown in Figure 2.
\begin{enumerate}[label=(\alph*)]
\item \begin{enumerate}[label=(\roman*)]
\item State the gradient of $l _ { 1 }$
\item Write down the $x$ coordinate of point $A$.

Another straight line $l _ { 2 }$ intersects $l _ { 1 }$ at the point $B$ with $x$ coordinate 1 and crosses the $x$-axis at the point $C$, as shown in Figure 2.

Given that $l _ { 2 }$ is perpendicular to $l _ { 1 }$
\end{enumerate}\item find an equation for $l _ { 2 }$ in the form $a x + b y + c = 0$, where $a$, b and $c$ are integers,
\item find the exact area of triangle $A B C$.
\end{enumerate}

\hfill \mbox{\textit{Edexcel C12 2017 Q6 [11]}}