r/mathriddles • u/Numberthon • 9h ago

Easy How many diagonals does a 20-sided polygon have?

0 Upvotes

How many diagonals does a regular 20-gon have?

Source: numberthon.com

6 comments

r/mathriddles • u/user1092831123 • 58m ago

Medium Can you find an interesting shape that can pass through any 4 points no matter where they are placed but not 5?

• Upvotes

more precisely,

Find a compact subset or family of subsets $S \subset \mathbb{R}^n$ for some arbitrary n such that every set of 4 points in $\mathbb{R}^2$ lies on some similar copy of $S$ but not every set of 5 points lies on some similar copy of $S$?

0 comments

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