Answer :
Write the matrix form of the function and solve:
[tex] \left|\begin{array}{ccc}x&y&1\\1&2&1\\2&5&1\end{array}\right|=0\\ \\ 2x+2y+5-4-y-5x=0\\ \\ -3x+1+y=0\\ \\ \boxed{y=3x-1}[/tex]
[tex] \left|\begin{array}{ccc}x&y&1\\1&2&1\\2&5&1\end{array}\right|=0\\ \\ 2x+2y+5-4-y-5x=0\\ \\ -3x+1+y=0\\ \\ \boxed{y=3x-1}[/tex]