Very simple question but I keep getting this wrong!
If you have two points e.g. $A(13, 6$) & $B(11, 12)$,
Using the gradient formula $m = \frac{(y_2 - y_1)}{(x_2 - x_1)}$ how do you know which of $A$ or $B$ corresponds to $(x_1, y_1)$?
I can work this out by drawing a diagram of the line. If the slope is negative, the higher of the two points is $(x_1, y_1)$. Otherwise the lower is.
But this takes too long in an exam. Is there a quicker way?
Thanks!