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Online Geometry Problem 661: Intersecting Circles,
Centers, Secant, Parallelogram. Level: High School,
Honors Geometry, College, Mathematics Education
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The figure shows the intersecting circles O
and O' at A and B. O'O extended and circle O meet at C. D is a point on
circle O', DA and DB meet circle O at E and F, respectively. Prove that
DECF is a parallelogram.
![Intersecting Circles, Parallelogram](p661_intersecting_circles.gif)
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