Paper 1, Section I, E

Linear Algebra | Part IB, 2018

State the Rank-Nullity Theorem.

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

dim⁡Im⁡(α)=dim⁡Im⁡(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:U→V\gamma: U \rightarrow V is another linear map, show that

dim⁡Im⁡(βα)+dim⁡Im⁡(αγ)⩽dim⁡Im⁡(α)+dim⁡Im⁡(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)

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