DA represents a vertical tower.

Points B, A, and C all lie in the same horizontal plane.

The angle of elevation of D at B is *x*�.

Angles BAC, BAD, and CAD are each 90�.

BD = BC and AD = AC.

Angle DBC is *y*�.

Prove that cos *y* = cos^{2}*x*.

DA represents a vertical tower.

Points B, A, and C all lie in the same horizontal plane.

The angle of elevation of D at B is *x*�.

Angles BAC, BAD, and CAD are each 90�.

BD = BC and AD = AC.

Angle DBC is *y*�.

Prove that cos *y* = cos^{2}*x*.