Worked example 3 Find the equation of each of following lines.
(i) Line parallel to a line with a slope of 3
Solution (i)
x y1
−1 − 2 y1
__ 4 through the point (−1, − 2 )
(ii) Line perpendicular to a line with a slope of − 2
__ 5 through the point ( 1, − 3 )
(ii) x y x1
1 − 3 y1
Recall that the perpendicular slope is the fi rst slope turned upside- down and with the opposite sign.
x1
Practice questions 21.1
1. Find the equation of each of the following lines, given the slope and the y -intercept. (i) Slope = − 3 ; y -intercept = 4 (ii) Slope = − 1 ; y -intercept = 0
(iii) Slope = 2 ; y -intercept = − 1
(iv) Slope = 1 (v) Slope = 2 (vi) Slope = − 3
(v) Slope = − 2 (vi) Slope = − 3
__ 5 ; y -intercept = 5
__ 3 ; y -intercept = − 7
__ 2 ; y -intercept = − 3
2. Find the equation of each of the following lines given the slope and a point on the line. (i) Slope = 5; point = (9, 2) (ii) Slope = − 6; point ( − 3, 6)