### Video Transcript

William drew an equilateral triangle with two sides whose sum equals 16 inches. Determine the length of the third side.

Let’s highlight the information we’re given. In William’s triangle, two sides’ sum equals 16 inches. This is not just any triangle though; it’s an equilateral triangle. What do we know about equilateral triangles?

In equilateral triangles, all sides are the same length. We know that two of the sides of this triangle add up to 16. We need to know what plus itself equals 16. We can also say two times some number equals 16. We know that two times eight equals 16; eight plus eight equals 16. So in his equilateral triangle, two sides’ sum equal 16, eight and eight.

We’re trying to determine the length of the third side. We know that this is an equilateral triangle, which means all the side lengths are the same. The first two side lengths were eight. That means that this third side will also be eight inches. In William’s equilateral triangle, every side is equal to eight inches.