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MathNet 2019-part-02 — 184 problems (EN–VI) Question 44

Math Olympiad Vault · MathNet 2019-part-02 — 184 problems (EN–VI)

Question 44

If $x$, $y$ and $z$ are positive real numbers and
$$
\frac{x y}{x+y}=a, \quad \frac{x z}{x+z}=b, \quad \text{and} \quad \frac{y z}{y+z}=c
$$
a) Verify that
$$
x=\frac{a y}{y-a}
$$
b) Verify that
$$
x=\frac{2 a b c}{a c+b c-a b}
$$