∴ Let the straight line L be: Ax+By+D=0.

The straight line l passes through the point A(x0, y0).

∴A×x0 + B×y0 + D=0

D=-Ax0 - By0

The straight line l is Ax+By-Ax0-By0=0.

That is: A(x-x0)+B(y-y0)=0.