Question: what is the formula y2-y1/x2-x1?
Answer: In math, the slope describes how steep a straight line is. It is sometimes called the gradient. The slope is defined as the "change in y" over the "change in x" of a line. If you pick two points on a line --- (x1,y1) and (x2,y2) --- you can calculate the slope by dividing y2 - y1 over x2 - x1.