Grade 11 2022 Problem 6

Neka su $a$, $b$ i $c$ redom duljine stranica trokuta nasuprot kutova veličina $\alpha$, $\beta$ i $\gamma$. Ako vrijedi $9a^2 + 9b^2 = 19c^2$, odredi $\dfrac{\mathrm{ctg}\,\gamma}{\mathrm{ctg}\,\alpha + \mathrm{ctg}\,\beta}$.