CAIE FP1 2018 June — Question 11 OR

Exam BoardCAIE
ModuleFP1 (Further Pure Mathematics 1)
Year2018
SessionJune
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Mark schemeDownload PDF ↗
TopicGroups
DifficultyHard +2.3 This is a linear algebra question from Further Mathematics requiring students to work with vector subspaces in R^4, likely involving finding a basis, dimension, or orthogonal complement. The multi-dimensional setting (R^4) and abstract nature of subspace problems requires sophisticated mathematical maturity beyond standard A-level. This is typical of the most challenging Further Maths content, requiring extended reasoning with advanced concepts.
Spec4.03r Solve simultaneous equations: using inverse matrix4.03s Consistent/inconsistent: systems of equations

Let \(V\) be the subspace of \(\mathbb { R } ^ { 4 }\) spanned by $$\mathbf { v } _ { 1 } = \left( \begin{array} { l } 1 \\ 2 \\ 0 \\ 2 \end{array} \right) , \quad \mathbf { v } _ { 2 } = \left( \begin{array} { r } - 2 \\ - 5 \\ 5 \\ 6 \end{array} \right) , \quad \mathbf { v } _ { 3 } = \left( \begin{array} { r } 0 \\ - 3 \\ 15 \\ 18 \end{array} \right) \quad \text { and } \quad \mathbf { v } _ { 4 } = \left( \begin{array} { r } 0 \\ - 2 \\ 10 \\ 8 \end{array} \right) .$$
  1. Show that the dimension of \(V\) is 3 . \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\)
  2. Express \(\mathbf { v } _ { 4 }\) as a linear combination of \(\mathbf { v } _ { 1 } , \mathbf { v } _ { 2 }\) and \(\mathbf { v } _ { 3 }\). \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\)
  3. Write down a basis for \(V\). \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) Let \(\mathbf { M } = \left( \begin{array} { r r r r } 1 & - 2 & 0 & 0 \\ 2 & - 5 & - 3 & - 2 \\ 0 & 5 & 15 & 10 \\ 2 & 6 & 18 & 8 \end{array} \right)\).
  4. Find the general solution of \(\mathbf { M x } = \mathbf { v } _ { 1 } + \mathbf { v } _ { 2 }\). \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) The set of elements of \(\mathbb { R } ^ { 4 }\) which are not solutions of \(\mathbf { M x } = \mathbf { v } _ { 1 } + \mathbf { v } _ { 2 }\) is denoted by \(W\).
  5. State, with a reason, whether \(W\) is a vector space. \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\) \(\_\_\_\_\)

Let $V$ be the subspace of $\mathbb { R } ^ { 4 }$ spanned by

$$\mathbf { v } _ { 1 } = \left( \begin{array} { l } 
1 \\
2 \\
0 \\
2
\end{array} \right) , \quad \mathbf { v } _ { 2 } = \left( \begin{array} { r } 
- 2 \\
- 5 \\
5 \\
6
\end{array} \right) , \quad \mathbf { v } _ { 3 } = \left( \begin{array} { r } 
0 \\
- 3 \\
15 \\
18
\end{array} \right) \quad \text { and } \quad \mathbf { v } _ { 4 } = \left( \begin{array} { r } 
0 \\
- 2 \\
10 \\
8
\end{array} \right) .$$

(i) Show that the dimension of $V$ is 3 .\\
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(ii) Express $\mathbf { v } _ { 4 }$ as a linear combination of $\mathbf { v } _ { 1 } , \mathbf { v } _ { 2 }$ and $\mathbf { v } _ { 3 }$.\\
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(iii) Write down a basis for $V$.\\
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Let $\mathbf { M } = \left( \begin{array} { r r r r } 1 & - 2 & 0 & 0 \\ 2 & - 5 & - 3 & - 2 \\ 0 & 5 & 15 & 10 \\ 2 & 6 & 18 & 8 \end{array} \right)$.\\
(iv) Find the general solution of $\mathbf { M x } = \mathbf { v } _ { 1 } + \mathbf { v } _ { 2 }$.\\
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The set of elements of $\mathbb { R } ^ { 4 }$ which are not solutions of $\mathbf { M x } = \mathbf { v } _ { 1 } + \mathbf { v } _ { 2 }$ is denoted by $W$.\\
(v) State, with a reason, whether $W$ is a vector space.\\
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\hfill \mbox{\textit{CAIE FP1 2018 Q11 OR}}