Maths Olympiad Prep

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Geometry Difficulty 4.8 AIME Find the answer

Let rectangle ABCDA B C D have lengths AB=20A B=20 and BC=12B C=12. Extend ray BCB C to ZZ such that CZ=18C Z=18. Let EE be the point in the interior of ABCDA B C D such that the perpendicular distance from EE to A\overline{A} B} is 6 and the perpendicular distance from EtoAD to \overline{A D} is 6 . Let line EZE Z intersect ABA B at XX and CDC D at YY. Find the area of quadrilateral AXYDA X Y D.

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

Solution

Draw the line parallel to A\overline{A} D}through through E,intersectingAB, intersecting \overline{A B} at FF and C\overline{C} D}at at G.Itisclearthat. It is clear that X F Eand and Y G E are congruent, so the area of A X Y Disequaltothatof is equal to that of A F G D.But. But A F G D is simply a 12 by 6 rectangle, so the answer must be 72 . (Note: It is also possible to directly compute the values of A Xand and D Y$, then use the formula for the area of a trapezoid.)

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