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)
The answer is 12.21 you find this by dividing 149 by ten and then 11 then 12 next 13 then realize you went too far and its some where around 12. somthing. I know that was confusing but thats the only way i can explain it or just put this into a calculator: