# Trigonometry/e to the i Pi

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Take the formula

- .

If radians, and so the formula becomes

or

a formula relating five key numbers in mathematics.

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< Trigonometry

The latest reviewed version was checked on *11 March 2011*. There is 1 pending change awaiting review.

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Take the formula

- $e^{xi}=\cos(x)+i\sin(x)$ .

If $x=\pi$ radians, $\cos(x)=-1$ and $\sin(x)=0$ so the formula becomes

- $e^{\pi i}=-1$

or

- $e^{\pi i}+1=0$

a formula relating five key numbers in mathematics.

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