Hi, I am learning about Polar Coordinates and how they can be written in several equivalent ways. I understand how you can add 360 to angles and use negative angles to represent the same point. However, I have a very hard time understanding how you can write the same point but with a negative distance r. So, the example in the book is r = 10 and θ = 30. I really can't see how r = -10 and θ = 210 is equivalent. Would anyone mind trying to give me some reasoning better than the one provided by my book? Thanks!