Trigonometric functions of the oriented angle

Periodicity of sin, cos: ( φ є R : sin (φ+2) = sin φ = sin (φ-2) cos (φ+2) = cos φ = cos (φ-2) sin = 1, sin = -1. cos 0 = 1, cos ( = -1. sin((/2) = 1, but there exists no ( ( ((/2; (/2+2() such that sin( =1 ( for cos . analogically ). That proves that 2is the minimal length of the interval of repetition ( sin, cos are ................
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