If pi shows up in the solution to a problem, this means that you can somehow transform the problem into a problem about circles.
In the famous Euler’s formula (e^(i*pi) = -1), the circle is quite obvious: Travelling halfway around the unit circle on the complex plane lands you at -1. (though the tricky part is showing why the e^i means travelling along the unit circle in the first place). For [other problems that involve pi](https://youtu.be/d-o3eB9sfls) the circle is a bit harder to find – but it’s there.
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