If P1(x1, y1)and P2(x2, y2)are two different points, then the slope of the line between them is;
If the slope of a line is zero (0) then the line is a horizontal line.
If the slope of a line is undefined, then the line is a vertical line.
ex.
Find the slope of the line, m, between A(-3,1) and B(4,6)