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Shanxi 20 10 Senior High School Entrance Examination Mathematics 18 Question Answers
As shown in the figure, in △ABC, AB = AC = 13, BC = 10, D is the midpoint of AB, and the intersection point D is DE⊥AC of point E, then the length of DE is _ _ _ _ _ _ _ _.

Make a vertical line BM⊥AC first, let CM be x, then AM is 13-x,

According to pythagorean theorem, that is, AB 2-AM 2 = BC 2-CM 2.

That is,100-x2 =169-(13-x) 2 solution, x=50/ 13.

bm^2=bc^2-cm^2= 120/ 13

Because d is the midpoint of AB, DE⊥AC,

Because BM⊥AC,

So △ADE is similar to△ △ABM.

So DE= 1/2BM=60/ 13.