Question 443778
Let a,b be the shortest two sides of a triangle, c the longest.

Then this must happen {{{ a + b > c }}} 
Assume that a=4 and b = 13.
Then {{{4+13 = 17 > c}}}
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Now assume short side 4 (call it b) and c = 13

Then {{{4 + b > 13}}}...{{{b > 9}}}
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Then given two sides, 4, 13, x: The possible values of x range {{{9<x<17}}}
between 9 and 17 (not inclusive).