general equation of a line is given by:
y=mx+b, where m is the slope of the line.
So, having this equation we need to isolate y to find the slope:
[tex]\begin{gathered} Ax-By=C \\ By=Ax-C \\ y=\frac{A}{B}x-\frac{C}{B} \end{gathered}[/tex]That would be the slope-intercept form of a line, that means A/B is the slope of the given line.
