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MathNet 2009-part-04 — 175 problems (EN–VI) Question 93

Math Olympiad Vault · MathNet 2009-part-04 — 175 problems (EN–VI)

Question 93

Show that
$$
\sqrt{\frac{|AB_1|}{|AB|}} + \sqrt{\frac{|BC_1|}{|BC|}} + \sqrt{\frac{|CA_1|}{|CA|}} \le \frac{3}{\sqrt{2}}
$$
if the incircle of a triangle $ABC$ touches the sides $BC$, $AC$ and $AB$ at the points $A_1$, $B_1$ and $C_1$, respectively.