Take the formula

- .

If radians, and so the formula becomes

or

a formula relating five key numbers in mathematics.

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.