What is the value of cos(−π)?

1 Answer
Zor Shekhtman
Aug 25, 2016

cos(−π)=−1

Explanation:

Consider a definition of a function cos(θ) on a unit circle as an abscissa (X-coordinate) of a point that lies on this unit circle and an angle from the positive direction of the X-axis to a radius to this point counterclockwise equals to θ.

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On this unit circle a point that corresponds to θ=−π has coordinates (−1,0) - this is th left most point on a circle.

Therfore, according to definition above, its abscissa is −1, which is the value of cos(−π).

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