In convex quadrilateral $ABCD$, $\angle A = \angle C$, $AB=CD=180$, and $AD \ne BC$.  The perimeter of $ABCD$ is 640. Find $\cos A$.
Question:
In convex quadrilateral $ABCD$, $\angle A = \angle C$, $AB=CD=180$, and $AD \ne BC$.  The perimeter of $ABCD$ is 640. Find $\cos A$.
Answer:
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In convex quadrilateral $ABCD$, $\angle A = \angle C$, $AB=CD=180$, and $AD \ne BC$.  The perimeter of $ABCD$ is 640. Find $\cos A$.
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