$$ \begin{align*} \textbf{Izračunaj ove izraze } \\ &\ a) x^{2} - 3x = \sqrt{x^{2}-2x+5} \\ &\ b) x^{2} - 3x = \sqrt{x^{2}-2x+5} \\ &\ c) \binom{21}{x}\sum_{x}^{x+12} \\ &\ d) x_{3} - \\ &\ \end{align*} $$