What's the better way to cut your sandwich—into triangles or rectangles? What shape gives you MORE sandwich? Use math to definitively solve the sandwich debate.

Discusses the properties and types of triangles, explaining that a triangle is a closed figure with three sides and angles. It categorizes triangles into equilateral, isosceles, scalene, obtuse ...

A version of this article appears in print on Aug. 27, 2019, Section D, Page 3 of the New York edition with the headline: How Many Triangles? Count on Math to Help.

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.