Answer :
To find out, suppose [tex](x_{1}, y_{1})[/tex] and [tex](x_{2} ,y_{2} )[/tex] are two points on the graph of
y = mx + b.
Then [tex]y_{1} =mx_{1} +b[/tex] and [tex]y_{2} =mx_{1} +b[/tex].
Use algebra to simplify [tex]\frac{y_{2} -y_{1} }{x_{1} -x_{2} }[/tex]
And give a geometric interpretation.
Hope this helps,
ROR