
Functions and Graphs 2-41
b. Given equation is, r = -8 cos q. This implies r
2
= -8r cos q.
Substituting the values of r and rcos q gives us the required result, i.e., x
2
+ y
2
= -8x.
2.6.2 Polar Equation of a Straight Line
The general equation of the straight line in the Cartesian coordinate system is
Ax + By + C = 0, (1)
where A, B and C are constants.
Let (r, q) be the polar coordinates of a point on the straight line referred to the origin as pole and the
x-axis as the initial line. Then, for any point (x, y) on the straight line x = r cos q, y = r sin q.
Substituting these in the equation of a straight line, we get
A (r cos q) + B (r sin ...