# Why is cos(pi) and cos (-pi) both equal to -1?

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Alan P.
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Apr 22, 2015

A full circle is

They are both equal to

because

if viewed as a unit circle centered on the Cartesian origin

the

and, at halfway around the unit circle,

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Triloshan T.
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Mar 30, 2017

#### Answer:

This is what a cosine graph looks like. Since

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graph{cos(x) [-4.76, 4.84, -2.64, 2.16]}

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Antoine
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Apr 22, 2015

One of the reasons is because

This means that

An example is the present case

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