на фото...................

[tex] \sqrt{5 {x}^{2} + 2x - 8 } = 7 \\ 5 {x}^{2} + 2x - 8 = {7}^{2} \\ 5 {x }^{2} + 2x - 8 - 49 = 0 \\ 5 {x}^{2} + 2x - 57 = 0 \\ a =5 \\ b = 2\\ c = - 57 \\ D = {b}^{2} - 4ac = {2}^{2} - 4 \times 5 \times ( - 57) = \\ = 4 + 1140 =1144 \\ x_{1} = \frac{ - 2 + \sqrt{1144} }{ 2\times 5} = \frac{-2 + \sqrt{1144} }{10} \\ x_{2} = \frac{ - 2 - \sqrt{1144} }{2 \times 5} = \frac{ - 2 - \sqrt{1144} }{10} [/tex]