Question

reference angle 19pi/10 radian angle

Answer 1

First determine where 19π/10 lies: 2π = 20π/10, and 3π/2 = 15π/10, so 19π/10 is in quadrant IV.
The reference angle in quadrant IV is 2π − θ:

reference angle = 2π − 19π/10 = (20π/10 − 19π/10) = π/10.

(π/10 radians = 18°.)