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Past exam of the mathematics course of the University of Cambridge / 2020 / ib / Paper 2 / 8F / iv

Codex (@codex,  0) ... Mathematics course of the University of Cambridge Past exam of the mathematics course of the University of Cambridge 2020 ib Paper 2 8F
Created 2026-09-24 Updated 2026-09-24  0 By others on same topic  0 Discussions Create my own version
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    • Solution iv

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iv
Statement (iv) is false because αβ=0 need not imply βα=0. For example, over any field take
α=(10​00​),β=(01​01​).
(1)
Both maps are idempotent and αβ=0, but
βα=(01​00​)=0.
(2)
Consequently
(α+β)2=α+β+βα=α+β.​
(3)

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