Answer:
[tex] { ( \sqrt{30 - x} )}^{2} = {x}^{2} \\ 30 - x = {x}^{2} \\ \\ {x}^{2} + x - 30 = 0 \\ delta = 1 - 4 \times ( - 30) \times 1 = 121 \\ x1 = \frac{ - 1 + \sqrt{121} }{2 \times 1} = \frac{ - 1 + 11}{2} = 5 \\ x2 = \frac{ - 1 - \sqrt{121} }{2 \times 1} = \frac{ - 1 - 11}{2} = - 6 \\ [/tex]
