Toán Lớp 8: Bik số tự nhiên a chia 3 dư 2. CMR: a^2 chia cho 3 dư 1
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Toán Lớp 8: Bik số tự nhiên a chia 3 dư 2. CMR: a^2 chia cho 3 dư 1
Comments ( 2 )
=>$a=3k+2$
=>$a^{2}$ = $(3k+2)^{2}$
=>$a^{2}$ = $9k^{2}$ + $12k$ +$4$
=>($9k^{2}$ + $12k$ +$4$) : $3$ = $3k^{2}$ + $4k$ + $1(dư 1)$
=>$a^{2}$ : 3 dư 1
Vậy $a^{2}$ : 3 dư 1