Toán Lớp 6: tìm x ∈ N
a, 2n + 5 chia hết cho n + 1
b, 3n + 2 chia hết cho n – 1
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Toán Lớp 6: tìm x ∈ N
a, 2n + 5 chia hết cho n + 1
b, 3n + 2 chia hết cho n – 1
Comments ( 2 )
a)2n+5⋮n+1
⇒2n+2+3⋮n+1
⇒2(n+1)+3⋮n+1
⇒3⋮n+1
⇒n+1=1;3⇒n=0;2
b) 3n+2 ⋮ n-1
⇒3n−3+5⋮n−1
⇒3(n−1)+5⋮n−1
⇒5⋮-1
⇒n-1=1;5⇒n=2;6
$ a) 2n + 5 ⋮ n+1 $
$ ⇒ 2n+2+3 ⋮ n+1 $
$ ⇒ 2(n+1)+3 ⋮ n+1 $
$ ⇒ 3 ⋮ n+1 $
$ ⇒ n+1=1;3 ⇒ n = 0;2 $
$ b) 3n+2 ⋮ n-1 $
$ ⇒ 3n-3+5 ⋮ n-1 $
$ ⇒ 3(n-1)+5 ⋮ n-1 $
$ ⇒ 5 ⋮ n-1 $
$ ⇒ n-1=1;5 ⇒ n=2;6 $