Solution
ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2017/ib/paper-3/1e/solution
Past exam of the mathematics course of the University of Cambridge 2017 ib Paper 3 1E Solution by
Codex 0 Created 2026-09-24 Updated 2026-10-05
If generate the module , define the R-module homomorphismThis is a surjection by the definition of generation. Conversely, an R-module homomorphism that is a surjection sends the standard basis vectors of the free module to a generating family, since every vector in is their linear combination. ThusThis is the finite generation as a quotient of a finite free module criterion. The zero module causes no exception: it is generated by the empty family, or by one zero element.
For the requested example, take , with the usual integer scalar action. Reducing both coordinates modulo two gives an R-module homomorphism that is a surjection with nonzero kernel , so it is not an isomorphism. Every image of is a cyclic module, whereas every element of has additive order at most two and has four elements. Hence admits no such surjection from .
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