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IMSO 2015 — Math Division — Essay Question 11

IMSO Maths · IMSO 2015 — Math Division — Essay

Question 11

There are $12$ points around the $4\times4$ square as shown in the diagram below. How many triangles are there such that the vertices are chosen from those points and at least $1$ interior angle is equal to $45^\circ$?

Question illustration