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 $m = (y_2 - y_1)/(x_2 - x_1)$ 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?