Let ABC be an isosceles triangle
with
. Point
is on
side
such that
. Point
is on side
such that
. Find the measure of
in degrees.
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Construct a line parallel to B C through D and call its intersection with A B , F . Connect F C and call its intersection with B D , G . Since △ A B C is isosceles and ∠ D B C = 6 0 ∘ , we know that △ B G C and △ F D G are equilateral triangles.Also notice that ∠ B E C = 5 0 ∘ which implies △ B E C is B-isosceles. Since △ B G C is equilateral, this implies that B E = B C = B G which implies that △ B E G is isosceles which implies that ∠ B G E = 8 0 ∘ . Due to supplementary angles, we find that ∠ F G E = 4 0 ∘ . Also notice that ∠ B F C = 4 0 ∘ which implies that △ E F G is isosceles which implies that F E G D is a kite which gives us an answer of 3 0 ∘ since the diagonals are perpendicular.