Because two of the angles are equal ( ) the point in the plane, , lies on the diagonal produced of the square base of the tower.
Therefore, in the diagram, .
Therefore, if the height and the breadth of the tower are and respectively:and
Therefore, using the Cosine Rule on :
Multiply both sides by :
Treating this as a quadratic in , and using the formula:
Grandad, since the other root is negative