## mathmath333 one year ago Count the number of triangles in the figure using permutation and combination

1. mathmath333

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2. mathmath333

\large \color{black}{\begin{align} & \normalsize \text{Count the number of triangles in the figure using }\hspace{.33em}\\~\\ & \normalsize \text{ permutation and combination}\hspace{.33em}\\~\\ \end{align}}

3. mathmath333

4. mathmate

I also got 28, but splitting it into permutations and combinations would be very messy! Hope someone would enlighten us on this!

5. Loser66

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6. mathmath333

yes counting manually is very easy

7. mathmath333

i doubt that there is a way P&C way

8. mathmate

The worry is if there are many panels in both dimensions, then it would be messy if we're not systematic.

9. ChillOut

I can only split in two cases - I can't fit the smallest triangles in a case where a formula applies. :(

10. mathmate

Yeah, then there are exterior and interior nodes, and the "invisible nodes" where the diagonal intersect... three sizes of triangles, we end up with about 9 or more cases!

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