1+cost+cos2t+cos3t=0
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