Решить тригонометричекое уравнение cos^2(x) = 1/2

                    cos²x=1/2
cosx=√1/2                     cosx=-√1/2
cosx=√2/2                     cosx=-√2/2
x1=+-π/4+2πn, n∈Z     x2=+-(π-π/4)+2πn, n∈Z
                                     x2=+-3π/4+2πn, n∈Z

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