A store's sign is the shape of an equilateral triangle. One side measures 21 inches. What is the length of each of the other two sides?

Equilaterial: all sides equal.

http://www.mathsisfun.com/triangle.html

Thank you very much...

You're welcome.

Please, though, use the same name for all of your posts.

To find the length of each of the other two sides of the equilateral triangle, we can use the fact that all three sides of an equilateral triangle are equal in length.

Given that one side of the equilateral triangle measures 21 inches, we can conclude that each of the other two sides will also have the same length.

Therefore, the length of each of the other two sides is also 21 inches.