Cho x,y,z $a,b\epsilon N*$ $(a\geq b)$ và a,b không $\vdots$ 5.
Cmr:$a^{4}-b^{4}\vdots 5$
Cho x,y,z $a,b\epsilon N*$ $(a\geq b)$ và a,b không $\vdots$ 5. Cmr:$a^{4}-b^{4}\vdots 5$
Started By mytran00, 21-10-2017 - 01:45
#2
Posted 23-10-2017 - 17:17
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Trung úy
Vì $a,b$ không chia hết cho 5 nên $a^{2},b^{2}\equiv 1,4(mod 5)$
=> $a^{4},b^{4}\equiv 1(mod5)$=> $a^{4}-b^{4}\vdots 5$
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