\(2a+1⋮x;2a+3⋮x\Leftrightarrow\left(2a+3\right)-\left(2a+1\right)⋮x\Leftrightarrow2⋮x\Leftrightarrow x\in\left\{+1;-1;+2;-2\right\}\)
Vì 2a+1 và 2a+3 đều lẻ nên:
\(x\ne2\)\(\Rightarrow x\in\left\{-1;1\right\}\)
cm voi moi so tu nhien n lon hon 3 thi n! cong 2009 khong phai la moi so chinh phuong