Missing angle

Geometry Level 4

The convex quadrilateral in the diagram has precisely 3 equal side lengths, and 2 of its interior angles are 10 8 108^\circ and 6 6 , 66^\circ, as shown. Find the acute angle labeled as "x" in degrees.


The answer is 60.

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2 solutions

Maria Kozlowska
Jul 2, 2017

First, let's create rhombus A B 1 C D AB_{1}CD . B C B 1 = B 1 A F = 6 \angle BCB_{1} = \angle B_{1}AF=6 . In C F E \triangle CFE , C F E = A F E = 60 \angle CFE = \angle AFE = 60 . This means that triangles B A F BAF and B 1 A F B_{1}AF are congruent therefore B A F = 6 \angle BAF=6 . This gives measure of B A D = ( 180 108 ) 2 6 = 60 \angle BAD=(180-108)-2*6=\boxed{60} .

Note:

There is a second solution to this problem: 132.

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