MA represents a vertical tower. Points A, B, and C lie in the same horizontal plane. MB and MC are wire stays, each of length 20 meters. The angle of elevation of M at B is x°. ∠MCB is z°, and ∠ABC = y° = ∠ACB.
- Prove that BC = 40 cos z.
- Show that BC = 40(cos x)(cos y).
- Calculate the magnitude of x if y = 42� and z = 71.8�.