How many triangles do you see in this image?

The magic formula explained simply
Looking for an elegant shortcut? For a large triangle divided into n segments arranged by lines parallel to the base (here n = 4), we can use the following formula:

T(n) = n × (n + 2) × (2n + 1) ÷ 8

Applied to n = 4:
T = 4 × 6 × 9 ÷ 8 = 27

This result corresponds perfectly to our step-by-step counting. The beauty of this formula is that it “counts” all possible dimensions, including multilevel combinations. Ideal for testing your intuition… or for silencing a heated debate!

 

 

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