Mark M. answered 03/11/21
Retired Math prof with teaching and tutoring experience in trig.
2tan2x - 3secx + 3 = 0
2(sec2x - 1) - 3secx + 3 = 0
2sec2x - 3secx + 1 = 0
(2secx - 1)(secx - 1) = 0
secx = 1/2 or secx = 1
So, cosx = 2 or cosx = 1
The equation cosx = 2 has no solution. cosx = 1 when x = 0 or 2π