Hello from MrBillDoesMath!
Answer:
@ = pi/3 (or 60 degrees) or @ = 7 pi/3 (or 420 degrees)
Discussion:
Let "@' denote the angle "theta". We are asked to find @ in the interval [0, 4 pi)
where
4cos(@) - 2 = 0. Adding 2 to both sides
4 cos(@) - 2 +2 = 2 =>
4 cos(@) = 2 Divide both sides by 4
cos(@) = 2/4 = 0.5
This implies that @ = pi/3 (or 60 degrees) or @ = (pi/3 + 2pi) = 7 pi/3 (or 420 degrees)
Thank you,
MrB