We spent forever arguing about the brain teaser that asks: How many triangles do you see? Here, mathematicians reveal the real answer. See if you’re right.

A Triangle Inequality. Billiards in triangles, which do not have the nice right-angled geometry of rectangles, is more complicated. As you might remember from high school geometry, there are several ...

By incorporating the high-low method and Orponen, Shmerkin and Wang’s work, Cohen, Pohoata and Zakharov have unmasked a new set of ties between the Heilbronn triangle problem and the rest of ...