June 2018 Paper 1 Q3
3 \(\mathbf{A} = \begin{pmatrix} 2 & 4 \\ 3 & -1 \end{pmatrix} \quad\) and \(\quad \mathbf{B} = \begin{pmatrix} -2 & 6 \\ 2 & 1 \end{pmatrix}\)
Work out \(\quad \mathbf{AB}\). [2 marks]
| Answer | Mark | Comments |
|---|---|---|
| \(\begin{pmatrix} 4 & 16 \\ -8 & 17 \end{pmatrix}\) | B2 | B1 for any two or three correct elements in the correct position in a \(2 \times 2\) matrix |
Additional guidance
| Correct answer followed by further work, eg \(\begin{pmatrix} 20 \\ 9 \end{pmatrix}\) scores B1 only Matrices multiplied the wrong way round can score SC1 if correct \(\mathrm{BA} = \begin{pmatrix} 14 & -14 \\ 7 & 7 \end{pmatrix}\) Condone no brackets around the numbers in their \(2 \times 2\) matrix Ignore any commas that appear in their \(2 \times 2\) matrix Do not follow through on any misreads of the numbers in the given matrices |