Question

2cos (t) +3 cos (t)+1=0

Answer 1

$5 \cos(t) = - 1$
es lo que resulta

Answer 2

2cos(t) + 3cos(t) + 1 = 0
5cos(t) = -1
cos(t) =  -1/5
 
hallando la solucion general

t=2$\pi$ +- arcocos(-1/5)