## Τετάρτη, 11 Οκτωβρίου 2017

### 2006 JBMO Shortlist 9

Let ${ABCD}$ be a trapezoid with ${AB // CD, AB > CD}$ and ${\angle A + \angle B = 90^\circ}$. Prove that the distance between the midpoints of the bases is equal to the semidifference of the bases.

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