[tex] \it 5|(x+2y)\ \ \ \ \ (1)\\ \\ 5|5(x+y) \Rightarrow 5|5x+5y\ \ \ \ \ (2)\\ \\ (1),\ (2) \Rightarrow 5|5x+5y-(x+2y) \Rightarrow 5|5x+5y-x-2y \Rightarrow 5|4x+3y [/tex]