Question

Tìm n biết 

a; 3n +19 chia hết cho n+1 

B; 2n+7 chia hết cho n+2

c; 6n+39 chia hết cho 2n+1 

Answer 1

a) \(3n+19⋮n+1\)

\(\Rightarrow\)\(3\left(n+1\right)+16⋮n+1\)

mà \(3\left(n+1\right)⋮n+1\)\(\Rightarrow\)\(16⋮n+1\)

\(\Rightarrow\)\(n+1\in\left\{1,-1,2,-2,4,-4,8,-8,16,-16\right\}\)

\(\Rightarrow n\in\left\{0,-2,1,-3,3,-5,7,-9,15,-17\right\}\)

b) \(2n+7⋮n+2\)

\(\Rightarrow2\left(n+2\right)+3⋮n+2\)

mà \(2\left(n+2\right)⋮n+2\Rightarrow3⋮n+2\)

\(\Rightarrow n+2\in\left\{1,3,-1,-3\right\}\)

\(\Rightarrow n\in\left\{-1,1,-3,-5\right\}\)

c)\(6n+39⋮2n+1\Rightarrow3\left(2n+1\right)+36⋮2n+1\)

mà\(3\left(2n+1\right)⋮2n+1\)\(\Rightarrow36⋮2n+1\)

\(\Rightarrow2n+1\in\left\{1,-1,2,-2,3,-3,4,-4,6,-6,9,-9,12,-12,18,-18,36,-36\right\}\)

\(\Rightarrow2n\in\left\{0,-2,1,-3,2,-4,3,-5,5,-7,8,-10,11,-13,17,-19,35,-37\right\}\)

\(\Rightarrow\)\(n\in\left\{0,-1,1,-2,4,-5\right\}\)