The diagonals of the quadrilateral ABDE meet at C. The segments AB and CE are of equal length 8 cm, and the segments AE and CD are also of equal length. The perimeter of the triangle CDE is 35 cm. Given that ∠BAC=∠AEC, find the perimeter of the pentagon ABCDE.
Solution
Using the condition of the problem, we get ∠BAE=∠BAC+∠CAE=∠AEC+∠CAE (Fig. 22). From the triangle ACE we get ∠AEC+∠CAE=∠DCE. Thus ∠BAE=∠DCE. At the same time, AE=CD and AB=CE. Consequently, the triangles AEB and CDE are equal, hence the perimeter of the triangle AEB is 35 cm.
Fig. 22
Now we get EA+AB+BC+CD+DE=(EA+AB+BE−CE)+(CD+DE+EC−CE)=(EA+AB+BE)+(CD+DE+EC)−2CE. Since EA+AB+BE=CD+DE+EC=35 cm and CE=8 cm, the perimeter of the pentagon ABCDE is 2⋅35 cm−2⋅8 cm=54 cm.
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