Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2018/iii/paper-138/2/b/i/solution

Let be a p-regular element, with eigenvalues on . On both acting on and acting on the dual representation , the eigenvalues are . Multiplicative lifts of roots of unity satisfy . Hence
All these identities concern the domain of a Brauer character, namely the p-regular elements. If necessary, extend the p-modular system to contain the relevant roots of unity and use one consistent choice of lifts.

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