Equilateral triangles have 3 congruent sides, so all 3 sides have the same length. Therefore, we know that . We are given the lengths of all 3 sides in terms of , but we only need to set two of them equal to each other to solve for . Let's use and to solve for . We know that , , and . Therefore, we can write the following equation to solve for
(Substitute given values into equation)
Solving for , we get:
(Subtract from both sides of the equation to isolate constants)
(Simplify)
(Subtract from both sides of the equation to isolate )
(Simplify)
(Divide both sides of the equation by to get rid of 's coefficient)