Paper 1, Section II, 6 A6 \mathrm{~A}

Vectors and Matrices
Part IA, 2013

Define the kernel and the image of a linear map α\alpha from Rm\mathbb{R}^{m} to Rn\mathbb{R}^{n}.

Let {e1,e2,,em}\left\{\mathbf{e}_{1}, \mathbf{e}_{2}, \ldots, \mathbf{e}_{m}\right\} be a basis of Rm\mathbb{R}^{m} and {f1,f2,,fn}\left\{\mathbf{f}_{1}, \mathbf{f}_{2}, \ldots, \mathbf{f}_{n}\right\} a basis of Rn\mathbb{R}^{n}. Explain how to represent α\alpha by a matrix AA relative to the given bases.

A second set of bases {e1,e2,,em}\left\{\mathbf{e}_{1}^{\prime}, \mathbf{e}_{2}^{\prime}, \ldots, \mathbf{e}_{m}^{\prime}\right\} and {f1,f2,,fn}\left\{\mathbf{f}_{1}^{\prime}, \mathbf{f}_{2}^{\prime}, \ldots, \mathbf{f}_{n}^{\prime}\right\} is now used to represent α\alpha by a matrix AA^{\prime}. Relate the elements of AA^{\prime} to the elements of AA.

Let β\beta be a linear map from R2\mathbb{R}^{2} to R3\mathbb{R}^{3} defined by

β(11)=(123),β(11)=(642)\beta\left(\begin{array}{l} 1 \\ 1 \end{array}\right)=\left(\begin{array}{l} 1 \\ 2 \\ 3 \end{array}\right), \quad \beta\left(\begin{array}{c} 1 \\ -1 \end{array}\right)=\left(\begin{array}{l} 6 \\ 4 \\ 2 \end{array}\right)

Either find one or more x\mathbf{x} in R2\mathbb{R}^{2} such that

βx=(121)\beta \mathbf{x}=\left(\begin{array}{c} 1 \\ -2 \\ 1 \end{array}\right)

or explain why one cannot be found.

Let γ\gamma be a linear map from R3\mathbb{R}^{3} to R2\mathbb{R}^{2} defined by

γ(120)=(13),γ(011)=(21),γ(010)=(01)\gamma\left(\begin{array}{l} 1 \\ 2 \\ 0 \end{array}\right)=\left(\begin{array}{l} 1 \\ 3 \end{array}\right), \quad \gamma\left(\begin{array}{l} 0 \\ 1 \\ 1 \end{array}\right)=\left(\begin{array}{c} -2 \\ 1 \end{array}\right), \quad \gamma\left(\begin{array}{l} 0 \\ 1 \\ 0 \end{array}\right)=\left(\begin{array}{l} 0 \\ 1 \end{array}\right)

Find the kernel of γ\gamma.