Concept:Count all triangles in the figure by grouping them by size – smallest, medium, and largest.Explanation:First, count the smallest triangles. There are 9 of them.Next, count triangles formed by combining two small triangles. There are 3 such triangles.Then, count triangles formed by combining four small triangles. There are 3 such triangles.No other triangles are present. Add all: 9 + 3 + 3 = 15 triangles.
