Find all polar coordinates of point p where p = (9 , -pi/5)

Adding any integer multiple of 2π to the direction argument will result in full-circle rotations, which are identities, so this family is equivalent to the give coordinates: 

(9, π/5 + 2nπ), for any integer n 

Also, multiplying the radius by -1 is a point reflection, equivalent to a half-turn rotation. Then add π to the direction for another half turn, and the result is another identity. So this too is equivalent to the given coordinates: 

(-9, π/5 + (2n + 1)π), for any integer n

40 & 50 in the right corner are the complementary angles as when placed in a sum (added together) they make 90°

The first one minimumi hope my answer you.