When the angle θ is greater than 90 degrees and less than 180 degrees, it is obvious that a
When θ=90 degrees, the intersection point is (0, 1), so sin90 degrees = 1, cos90 degrees =0, tan90 degrees = 1/0, infinity.
When θ=0 degrees, the intersection point is (1, 0), so sin0=0, cos0= 1, tan0 = 0= 0;
When θ= 180 degrees, the intersection point is (-1 0), so sin 180 degrees =0, cos 180 degrees =- 1, tan 180 degrees =