Question

tim n thuoc N

a,n+2 chia het cho 3n+5

b,n²-2n+9 chia het cho n-2

c,3n+7 chia het cho n-2

Answer 1

a \(n+2⋮3n+5\)

\(\Rightarrow3\left(n+2\right)⋮3n+5\)

\(\Rightarrow3n+5+1⋮3n+5\)

\(\Rightarrow1⋮3n+5\)

\(\Rightarrow3n+5\in\left\{1,-1\right\}\)

\(\Rightarrow n=-2\)(loại)

c \(3n+7⋮n-2\)

\(\Rightarrow2\left(3n+7\right)⋮n-2\)

\(\Rightarrow6n+14⋮n-2\)

\(\Rightarrow3\left(n-2\right)+20⋮n-2\)

\(\Rightarrow20⋮n-2\)

\(\Rightarrow n-2\in\left\{20,1,10,2,5,4,-20,-1,-10,-2,-5,-4\right\}\)

...(như câu a)

Answer 2

câu b đâu