1+cost+cos2t+cos3t=0

1+сos2t+2cos2tcost=02cos²t+2cos2tcost=02cost(cost+cos2t)=02cost*2cod3t/2cost/2=0cost=0⇒t=π/2+πncos3t/2=0⇒3t/2=π/2+πn⇒t=π/3+2πn/3cost/2=0⇒t=π+2πn