$\dfrac{ab}{a^2 + b^2}$.
$x^3 + y^3 - 6xy + 8 = 0$.
$a - b = \sqrt{1 - b^2} - \sqrt{1 - a^2}$.
$a^2 + b^2 = 1$.
$4x^2 + 14x + 11 = 4\sqrt{6x + 10}$.
$\dfrac{(a + b)^2}{ab} + \dfrac{(b + c)^2}{bc} + \dfrac{(c + a)^2}{ca}$
$9 + 2(\dfrac{a}{b + c} + \dfrac{b}{c + a} + \dfrac{c}{a + b})$.
Sin$\dfrac{A}{2}$ $\dfrac{a}{2\sqrt{bc}}$.
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