1/tg^2(x)=cos^2(x)/sin^2(x)=(1-sin^2(x))/sin^2(x)=1/sin^2(x) - 1
Замена 1/sin(x) = t,
t^2 - 1 +3t +3 =0
t^2 + 3t + 2 = 0
t = -1 или t = -2
sin x = -1 или sin x = -1/2
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