In an isosceles triangle ABC , AB=AC and angle BAC =120 degree. Points D and E lie on BC such that BD=DE=EC . Prove that ADE is an equilateral triangle .
Hello thereddevilsThere's nothing wrong with the question. Just use some simple trigonometry and Pythagoras' Theorem.
Let , and then if is the mid-point of :Also
So using Pythagorasand hence is equilateral.
(by symmetry)
Grandad