n2+n+4 chia het cho n+1 ta co:
n2+n+4
= n.n+n+4
=n . ( n+1) +4
vi : n. ( n+1) chia het cho n+1
\(\Rightarrow\)4chia het cho n+1
n+1 E U(4) = { 1;2;4}
n+1 = 1\(\Rightarrow\)n= 1-1 =0
n+1 =2\(\Rightarrow\)n =2-1=1
n+1 =4\(\Rightarrow\)n= 4-1 = 3
vay n E {0;1;3}
tick minh nha