help solve trig function interval [0,2pi)

Answer 1

First, solve the quadratic equation to get:

cos(t) = 1/3, -5/6

cos(t) = 1/3:

t is in the 1st quadrant, or the 4th

angle is t or 2pi - t

cos(t) = -5/6:

t is in the 3rd or 4th quadrant

v = acos (+5/6)

t = pi +/- v