Paper 1, Section I, E

Linear Algebra
Part IB, 2018

State the Rank-Nullity Theorem.

If α:VW\alpha: V \rightarrow W and β:WX\beta: W \rightarrow X are linear maps and WW is finite dimensional, show that

dimIm(α)=dimIm(βα)+dim(Im(α)Ker(β))\operatorname{dim} \operatorname{Im}(\alpha)=\operatorname{dim} \operatorname{Im}(\beta \alpha)+\operatorname{dim}(\operatorname{Im}(\alpha) \cap \operatorname{Ker}(\beta))

If γ:UV\gamma: U \rightarrow V is another linear map, show that

dimIm(βα)+dimIm(αγ)dimIm(α)+dimIm(βαγ)\operatorname{dim} \operatorname{Im}(\beta \alpha)+\operatorname{dim} \operatorname{Im}(\alpha \gamma) \leqslant \operatorname{dim} \operatorname{Im}(\alpha)+\operatorname{dim} \operatorname{Im}(\beta \alpha \gamma)