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2006 Romanian NMO Problems/Grade 7/Problem 3

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Problem

In the acute-angle triangle ABC we have \angle ACB = 45^\circ. The points A_1 and B_1 are the feet of the altitudes from A and B, and H is the orthocenter of the triangle. We consider the points D and E on the segments AA_1 and BC such that A_1D = A_1E = A_1B_1. Prove that

a) A_1B_1 = \sqrt{ \frac{A_1B^2+A_1C^2}{2} };

b) CH=DE.

Solution

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