In the figure below, ABCD is a concave
quadrilateral, where AD = CD = BC, and angle C = 2 times angle
A. Prove that x is equal to: 120 degrees minus angle A. Try to
use elementary geometry (such as Euclid's Elements)
Geometry Problem 4
Concave quad it is, AD, CD, and BC equals, Angle C
twice of A, Prove x equals onetwenty minus A, With
Euclid's Elements, this problem we seal.
See solution below
See
also: Art 01
Problem 42.
