This is our line: $f(x)=2x-5$

I have to find a point on this line that is the closest to the point $P(1,2)$. How do I go on about solving this? Should I use derivative and distance from the point to the line? I've done this so far:

$d\to$ distance between $P(1,2)$ and $f(x)$

$d= \sqrt{(x\_2-x\_1)^2+(y\_2-y\_1)^2}$

But how do I get the $x\_2,y\_2 $ from $f(x)$?