maths
posted by Anonymous .
ABC is a triangle with ∠BAC=60∘,AB=5 and AC=25. D is a point on the internal angle bisector of ∠BAC such that BD=DC. What is AD^2?

using the law of cosines, if we let AD=x,
x^2 + 5^2  2x(5)cos30 = x^2 + 25^2  2x(25)cos30
255x√3 = 62525x√3
20x√3 = 600
x = 30/√3
x^2 = 300