Question 1203823

2 cos^2(t) − cos(t) = 1

2 cos^2(t) − cos(t) - 1=0

2cos^2t-2cost+cost-1=0

2cost(cost -1)+1(cost-1)=0

(2cost+1)(cost-1)=0

If 2cost +1=0 
2cost = -1
cost =-1/2


cost-1 = 0

cost =1

From above 
This is true when 

t =0,2pi/3,4pi/3