Paper 1, Section II, G

Groups, Rings and Modules | Part IB, 2013

(i) Consider the group G=GL2(R)G=G L_{2}(\mathbb{R}) of all 2 by 2 matrices with entries in R\mathbb{R} and non-zero determinant. Let TT be its subgroup consisting of all diagonal matrices, and NN be the normaliser of TT in GG. Show that NN is generated by TT and (0110)\left(\begin{array}{ll}0 & 1 \\ 1 & 0\end{array}\right), and determine the quotient group N/TN / T.

(ii) Now let pp be a prime number, and FF be the field of integers modulo pp. Consider the group G=GL2(F)G=G L_{2}(F) as above but with entries in FF, and define TT and NN similarly. Find the order of the group NN.

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