17^2 = 289 18^2 = 324 Any of the numbers between 289 and 324 exclusive will have a root between 17 and 18 Eg sr(300) = 17.3205... is between 17 and 18 on the number line. There are 33 other whole number answers you could pick
Suppose first that is a normal subgroup. Then by definition we must have for all , for every . Let and choose (). By hypothesis we have , i.e. for some , thus . So we have . You can prove in the same way.
Suppose for all . Let , we have to prove for every . So, let . We have that for some (by the hypothesis). hence we have . Because was chosen arbitrarily we have the desired
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