In consequence, the Angle-Angle (AA) Similarity Postulate leads us to conclude that △ ABC ~ △ A'B'C'. This allows us to write the following proportion.
BC/B'C' = AC/A'C'
Finally, let's rewrite the proportion above in an equivalent way.
BC/AC = B'C'/A'C' = Rise/Run = m
We have seen that no matter the points we pick to find the slope of a line, it will always be the same.
The slope of line l through A and B, which is BCAC, is equal to B'C'A'C', the slope of the line l through A' and B'.
