1. The denominator says the the top half of the circle should be divided into 7 pieces.
2. The numerator says go to the 4th piece starting from (1, 0)
3. This angle is the 2nd quadrant so the signs are (−, +) for (x, y).
Move clockwise from (1, 0).
Divide half of the circle into 9 pieces. Every 18 pieces is one time around the circle.
−21π intersects the unit circle at the point (−1, 0), so the signs of the coordinates are (−, 0).