In triangle ABC, AB = AC and angle A is equal to 36˚ Point D is on AC so that BD bisects
(a) Prove that BC = BD = AD.
(b) Let x = BC and let y = CD. Using similar triangles BCD and ABC, write an equation involving x and y.
(c) Let r = y/x. Write the equation from Part (b) in terms of r and find r
(d) Find cos 36˚ and cos 72˚ using Parts a-c. (Do not use your calculator!)