What’s your favorite proof accessible to a general audience? [closed]

What math statement with proof do you find most beautiful and elegant, where such is accessible to a general audience, meaning you could state, prove, and explain it to a general audience in roughly $5 \pm\epsilon$ minutes.
Let’s define ‘general audience’ as approximately an average adult with education and experience comparable to someone holding a bachelor’s degree in any non science major (e.g. history) from an average North American university.

Answer

I really like the proof of in which $1 + 2 + \cdots + (n-1) + n$ is written forwards then backwards and summed. It is claimed that Gauss had come up with this when he was just a child, although contested.

The proof

Let
Clearly,

Sum to get

Hence, and

Attribution
Source : Link , Question Author : Community , Answer Author : Community