Edexcel C4 2016 June — Question 8 15 marks

Exam BoardEdexcel
ModuleC4 (Core Mathematics 4)
Year2016
SessionJune
Marks15
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicVectors 3D & Lines
TypeArea of parallelogram or trapezium using vectors
DifficultyStandard +0.3 This is a straightforward multi-part vectors question testing standard techniques: substituting into a line equation, writing parallel line equations, distance between points, angle between vectors, and finding points at a given distance. All parts follow routine procedures with no novel problem-solving required, making it slightly easier than average.
Spec1.10a Vectors in 2D: i,j notation and column vectors1.10b Vectors in 3D: i,j,k notation1.10c Magnitude and direction: of vectors1.10f Distance between points: using position vectors4.04c Scalar product: calculate and use for angles

8. With respect to a fixed origin \(O\), the line \(l _ { 1 }\) is given by the equation $$\mathbf { r } = \left( \begin{array} { r } 8 \\ 1 \\ - 3 \end{array} \right) + \mu \left( \begin{array} { r } - 5 \\ 4 \\ 3 \end{array} \right)$$ where \(\mu\) is a scalar parameter.
The point \(A\) lies on \(l _ { 1 }\) where \(\mu = 1\)
  1. Find the coordinates of \(A\). The point \(P\) has position vector \(\left( \begin{array} { l } 1 \\ 5 \\ 2 \end{array} \right)\).
    The line \(l _ { 2 }\) passes through the point \(P\) and is parallel to the line \(l _ { 1 }\)
  2. Write down a vector equation for the line \(l _ { 2 }\)
  3. Find the exact value of the distance \(A P\). Give your answer in the form \(k \sqrt { 2 }\), where \(k\) is a constant to be determined. The acute angle between \(A P\) and \(l _ { 2 }\) is \(\theta\).
  4. Find the value of \(\cos \theta\) A point \(E\) lies on the line \(l _ { 2 }\) Given that \(A P = P E\),
  5. find the area of triangle \(A P E\),
  6. find the coordinates of the two possible positions of \(E\).

Question 8:
Part (a):
AnswerMarks Guidance
AnswerMark Guidance
\(A(3,5,0)\)B1 \((3,5,0)\)
Part (b):
AnswerMarks Guidance
AnswerMark Guidance
\(\{l_2:\}\,\mathbf{r}=\begin{pmatrix}1\\5\\2\end{pmatrix}+\lambda\begin{pmatrix}-5\\4\\3\end{pmatrix}\)M1 \(\mathbf{a}+\lambda\mathbf{d}\) or \(\mathbf{a}+\mu\mathbf{d}\), \(\mathbf{a}+t\mathbf{d}\), \(\mathbf{a}\neq\mathbf{0}\), \(\mathbf{d}\neq\mathbf{0}\), with either \(\mathbf{a}=\mathbf{i}+5\mathbf{j}+2\mathbf{k}\) or \(\mathbf{d}=-5\mathbf{i}+4\mathbf{j}+3\mathbf{k}\), or a multiple of \(-5\mathbf{i}+4\mathbf{j}+3\mathbf{k}\)
Correct vector equation using \(\mathbf{r}=\) or \(l=\) or \(l_2=\)A1 Do not allow \(l_2\): or \(l_2\rightarrow\) or \(l_1=\) for the A1 mark
Part (c):
AnswerMarks Guidance
AnswerMark Guidance
\(\overrightarrow{AP}=\overrightarrow{OP}-\overrightarrow{OA}=\begin{pmatrix}1\\5\\2\end{pmatrix}-\begin{pmatrix}3\\5\\0\end{pmatrix}=\begin{pmatrix}-2\\0\\2\end{pmatrix}\)M1 Full method for finding \(AP\)
\(AP=\sqrt{(-2)^2+(0)^2+(2)^2}=\sqrt{8}=2\sqrt{2}\)A1 \(2\sqrt{2}\)
Part (d):
AnswerMarks Guidance
AnswerMark Guidance
\(\overrightarrow{AP}\cdot\mathbf{d}_2\) requiredM1 Realisation that the dot product is required between \((\overrightarrow{AP}\) or \(\overrightarrow{PA})\) and \(\pm K\mathbf{d}_2\) or \(\pm K\mathbf{d}_1\)
\(\cos\theta=\frac{\overrightarrow{AP}\cdot\mathbf{d}_2}{\overrightarrow{AP}
\(\cos\theta=\frac{\pm(10+0+6)}{\sqrt{8}\cdot\sqrt{50}}=\frac{4}{5}\)A1 cso \(\cos\theta=\frac{4}{5}\) or \(0.8\) or \(\frac{8}{10}\) or \(\frac{16}{20}\)
Part (e):
AnswerMarks Guidance
AnswerMark Guidance
\(\text{Area }APE=\frac{1}{2}(\text{their }2\sqrt{2})^2\sin\theta\)M1 \(\frac{1}{2}(\text{their }2\sqrt{2})^2\sin\theta\) or \(\frac{1}{2}(\text{their }2\sqrt{2})^2\sin(\text{their }\theta)\)
\(=2.4\)A1 \(2.4\) or \(\frac{12}{5}\) or \(\frac{24}{10}\) or awrt \(2.40\)
Part (f):
AnswerMarks Guidance
AnswerMark Guidance
\(\overrightarrow{PE}=(-5\lambda)\mathbf{i}+(4\lambda)\mathbf{j}+(3\lambda)\mathbf{k}\) and \(PE=\text{their }2\sqrt{2}\) from part (c)
\((-5\lambda)^2+(4\lambda)^2+(3\lambda)^2=(\text{their }2\sqrt{2})^2\)M1 This mark can be implied
\(50\lambda^2=8\Rightarrow\lambda^2=\frac{4}{25}\Rightarrow\lambda=\pm\frac{2}{5}\)A1 Either \(\lambda=\frac{2}{5}\) or \(\lambda=-\frac{2}{5}\)
Substitutes at least one value of \(\lambda\) into \(l_2\)dM1 Dependent on previous M mark
\(\{\overrightarrow{OE}\}=\begin{pmatrix}3\\\frac{17}{5}\\4\end{pmatrix}\) or \(\begin{pmatrix}3\\3.4\\0.8\end{pmatrix}\), \(\{\overrightarrow{OE}\}=\begin{pmatrix}-1\\\frac{33}{5}\\\frac{16}{5}\end{pmatrix}\) or \(\begin{pmatrix}-1\\6.6\\3.2\end{pmatrix}\)A1 At least one set of coordinates correct
Both sets of coordinates correctA1
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# Question 8:

## Part (a):

| Answer | Mark | Guidance |
|--------|------|----------|
| $A(3,5,0)$ | B1 | $(3,5,0)$ |

## Part (b):

| Answer | Mark | Guidance |
|--------|------|----------|
| $\{l_2:\}\,\mathbf{r}=\begin{pmatrix}1\\5\\2\end{pmatrix}+\lambda\begin{pmatrix}-5\\4\\3\end{pmatrix}$ | M1 | $\mathbf{a}+\lambda\mathbf{d}$ or $\mathbf{a}+\mu\mathbf{d}$, $\mathbf{a}+t\mathbf{d}$, $\mathbf{a}\neq\mathbf{0}$, $\mathbf{d}\neq\mathbf{0}$, with either $\mathbf{a}=\mathbf{i}+5\mathbf{j}+2\mathbf{k}$ or $\mathbf{d}=-5\mathbf{i}+4\mathbf{j}+3\mathbf{k}$, or a multiple of $-5\mathbf{i}+4\mathbf{j}+3\mathbf{k}$ |
| Correct vector equation using $\mathbf{r}=$ or $l=$ or $l_2=$ | A1 | Do not allow $l_2$: or $l_2\rightarrow$ or $l_1=$ for the A1 mark |

## Part (c):

| Answer | Mark | Guidance |
|--------|------|----------|
| $\overrightarrow{AP}=\overrightarrow{OP}-\overrightarrow{OA}=\begin{pmatrix}1\\5\\2\end{pmatrix}-\begin{pmatrix}3\\5\\0\end{pmatrix}=\begin{pmatrix}-2\\0\\2\end{pmatrix}$ | M1 | Full method for finding $AP$ |
| $AP=\sqrt{(-2)^2+(0)^2+(2)^2}=\sqrt{8}=2\sqrt{2}$ | A1 | $2\sqrt{2}$ |

## Part (d):

| Answer | Mark | Guidance |
|--------|------|----------|
| $\overrightarrow{AP}\cdot\mathbf{d}_2$ required | M1 | Realisation that the dot product is required between $(\overrightarrow{AP}$ or $\overrightarrow{PA})$ and $\pm K\mathbf{d}_2$ or $\pm K\mathbf{d}_1$ |
| $\cos\theta=\frac{\overrightarrow{AP}\cdot\mathbf{d}_2}{|\overrightarrow{AP}||\mathbf{d}_2|}=\frac{\pm\left(\begin{pmatrix}-2\\0\\2\end{pmatrix}\cdot\begin{pmatrix}-5\\4\\3\end{pmatrix}\right)}{\sqrt{(-2)^2+(0)^2+(2)^2}\cdot\sqrt{(-5)^2+(4)^2+(3)^2}}$ | dM1 | Dependent on previous M mark. Applies dot product formula between their $(\overrightarrow{AP}$ or $\overrightarrow{PA})$ and $\pm K\mathbf{d}_2$ or $K\mathbf{d}_1$ |
| $\cos\theta=\frac{\pm(10+0+6)}{\sqrt{8}\cdot\sqrt{50}}=\frac{4}{5}$ | A1 cso | $\cos\theta=\frac{4}{5}$ or $0.8$ or $\frac{8}{10}$ or $\frac{16}{20}$ |

## Part (e):

| Answer | Mark | Guidance |
|--------|------|----------|
| $\text{Area }APE=\frac{1}{2}(\text{their }2\sqrt{2})^2\sin\theta$ | M1 | $\frac{1}{2}(\text{their }2\sqrt{2})^2\sin\theta$ or $\frac{1}{2}(\text{their }2\sqrt{2})^2\sin(\text{their }\theta)$ |
| $=2.4$ | A1 | $2.4$ or $\frac{12}{5}$ or $\frac{24}{10}$ or awrt $2.40$ |

## Part (f):

| Answer | Mark | Guidance |
|--------|------|----------|
| $\overrightarrow{PE}=(-5\lambda)\mathbf{i}+(4\lambda)\mathbf{j}+(3\lambda)\mathbf{k}$ and $PE=\text{their }2\sqrt{2}$ from part (c) | — | — |
| $(-5\lambda)^2+(4\lambda)^2+(3\lambda)^2=(\text{their }2\sqrt{2})^2$ | M1 | This mark can be implied |
| $50\lambda^2=8\Rightarrow\lambda^2=\frac{4}{25}\Rightarrow\lambda=\pm\frac{2}{5}$ | A1 | Either $\lambda=\frac{2}{5}$ or $\lambda=-\frac{2}{5}$ |
| Substitutes at least one value of $\lambda$ into $l_2$ | dM1 | Dependent on previous M mark |
| $\{\overrightarrow{OE}\}=\begin{pmatrix}3\\\frac{17}{5}\\4\end{pmatrix}$ or $\begin{pmatrix}3\\3.4\\0.8\end{pmatrix}$, $\{\overrightarrow{OE}\}=\begin{pmatrix}-1\\\frac{33}{5}\\\frac{16}{5}\end{pmatrix}$ or $\begin{pmatrix}-1\\6.6\\3.2\end{pmatrix}$ | A1 | At least one set of coordinates correct |
| Both sets of coordinates correct | A1 | — |

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8. With respect to a fixed origin $O$, the line $l _ { 1 }$ is given by the equation

$$\mathbf { r } = \left( \begin{array} { r } 
8 \\
1 \\
- 3
\end{array} \right) + \mu \left( \begin{array} { r } 
- 5 \\
4 \\
3
\end{array} \right)$$

where $\mu$ is a scalar parameter.\\
The point $A$ lies on $l _ { 1 }$ where $\mu = 1$
\begin{enumerate}[label=(\alph*)]
\item Find the coordinates of $A$.

The point $P$ has position vector $\left( \begin{array} { l } 1 \\ 5 \\ 2 \end{array} \right)$.\\
The line $l _ { 2 }$ passes through the point $P$ and is parallel to the line $l _ { 1 }$
\item Write down a vector equation for the line $l _ { 2 }$
\item Find the exact value of the distance $A P$.

Give your answer in the form $k \sqrt { 2 }$, where $k$ is a constant to be determined.

The acute angle between $A P$ and $l _ { 2 }$ is $\theta$.
\item Find the value of $\cos \theta$

A point $E$ lies on the line $l _ { 2 }$ Given that $A P = P E$,
\item find the area of triangle $A P E$,
\item find the coordinates of the two possible positions of $E$.
\end{enumerate}

\hfill \mbox{\textit{Edexcel C4 2016 Q8 [15]}}