Triangle Thingamajig

How many triangles are there in the figure above?

14 8 10 12

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1 solution

Vignesh S
Apr 12, 2016

Just count them, there are not many of them. But if there were many, you could use ( n 3 ) \dbinom{n}{3} - ( r 3 ) \dbinom{r}{3} suitably (where r r points out of n n are collinear)

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