Tìm n E Z a, n-7 chia hế 2n+3 b, n^2-2 chia heegs cho n+3

1 bình luận về “Tìm n E Z a, n-7 chia hế 2n+3 b, n^2-2 chia heegs cho n+3”

1. a) n-7 \vdots 2n+3

   => 2n-14 \vdots 2n+3

   => 2n+3-17 \vdots 2n+3

   => 17 \vdots 2n+3

   => 2n+3 in {+-1 ; +-17}

   => n in {-1 ; -2 ; 7 ; -10}

   b) n^2 – 2 \vdots n+3

   => n^2 + 3n – 3n – 9 +7 \vdots n+3

   => n(n+3) – 3(n+3) + 7 \vdots n+3

   => (n-3)(n+3) + 7 \vdots n+3

   => 7 \vdots n+3

   => n+3 in {+-1 ; +-7}

   => n in {-2 ; -4 ; 4 ; -10}

   Vậy n in {-2 ; 4 ; -4 ; -10}

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