Question 673022
Find all t in the interval [0, 2π] satisfying (cos t)2 + 4 cos t + 3 = 0.
cos ^2 t+4cos t+3=0
(cos t+3)(cos t+1)=0
cos t+3=0
cos t=-3 (reject, (-1 ≤ cos t ≤1)
(cos t+1)=0
cos t=-1
t=π