By the definition of the trigonometric functions,
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(1)
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(2)
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(3)
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(4)
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(5)
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(6)
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Trigonometry Angles--0
See also
Trigonometry Angles, TrigonometryExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Trigonometry Angles--0." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/TrigonometryAngles0.html