1. Point-slope Form of Equations of Straight Lines

2. How can we find the equation of L?
Suppose we are given a point A(x1, y1) on a straight line L with slope m.
How can we find the equation of L?
Let P(x, y) be a point on L.
Slope of AP
= slope of L
y – y1
i.e. m =
x – x1
y – y1 = m(x – x1)

3. Point-slope Form
The equation of L passing through A(x1, y1) with slope m is given by:
y – y1 = m(x – x1)

4. Follow-up question
Find the equation of the straight line passing through (–1, 6) with slope –2.
The equation of the straight line is
y - 6 = -2[x - (-1)]
y - 6 = -2x - 2
 y = -2x + 4
 y – y1 = m(x – x1)