Start by finding *r* at the endpoints. When θ = 0, r = cos0 = 1.
When ,
As θ moves from 0 to , the value of r = cos θ decreases from 1 to 0.
When , r = 0. When θ = π, r = cosπ = -1. Remembering how we graph polar coordinates with negative *r*, we find these points: When θ is in the second quadrant and *r* is negative, the point (r,θ) is in the fourth quadrant. As θ moves closer to π, the points (r,θ) move closer to the positive *x*-axis. As θ moves from to π, the value r = cosθ goes from 0 to -1. The points (r,θ) move further from the origin as θ gets closer to π. To graph r = cosθ for 0≤ θ≤ π we put the graphs from (a) and (b) together: |