Can any kind soul help me in the below?

Find z between 0 and 360 degrees which satisfy the equation.

1. sec^2 z = 4 sec z - 3

Answer:

sec^2 z = 4 sec z - 3

sec^2 z - 4 sec z + 3 = 0

(sec z - 3)( sec z - 1) = 0

sec z = 3 or sec z = 1

cos z = 1/3 or cos z = 1

z = 70.5 deg, z = 0, 360 deg(rejected)

cos is positive => so in 1st or 4th quadrant

z = 70.5, 360-70.5

= 70.5, 289.5

My question: why is z = 360 deg rejected?

why is z = 0 deg not rejected?