A line passes through (x1, y1) and (h, k). If slope of the line is m, show that k−y1=m(h−x1).
Let A(x1, y1) and B(h, k) be two points.
∴ Slope of AB=k−y1h−x1
Slope of AB = m (given)
∴ m=k−y1h−x1 ⇒ k−y1=m(h−x1)
The slope of a line joining the points (x1,y1) and (x2,y2) is y1−y2x1−x2.