Question

1+cost+cos2t+cos3t=0

Answer 1

1+сos2t+2cos2tcost=0
2cos²t+2cos2tcost=0
2cost(cost+cos2t)=0
2cost*2cod3t/2cost/2=0
cost=0⇒t=π/2+πn
cos3t/2=0⇒3t/2=π/2+πn⇒t=π/3+2πn/3
cost/2=0⇒t=π+2πn