Ответ:

[tex]1) {x}^{2} - 25 = 0 \\ (x - 5)(x + 5) = 0 \\ x1 = 5 \\ x2 = - 5[/tex]

[tex]2) {x}^{2} + 3x = 0 \\ x(x + 3) = 0 \\ x1 = 0 \\ x2 = - 3[/tex]

[tex]3)2 {x}^{2} + x - 8 = 0 \\ d = 1 - 4 \times 2 \times ( - 8) \\ d = 1 + 64 \\ d = 65[/tex]

[tex]4)2 {x}^{2} - 5x + 2 = 0 \\ d = 25 - 4 \times 2 \times 2 \\ d = 25 - 16 \\ d = 9 \\ \sqrt{d} = 3 \\ x1 = \frac{5 - 3}{4} = \frac{2}{4} = 0.5 \\ x2 = \frac{5 + 3}{4} = \frac{8}{4} = 2[/tex]

[tex]5) {x}^{2} - 5x - 40 = 0 \\ x1x2 = - 40 \\ x1 + x2 = 5[/tex]

[tex]6) {x}^{2} + 8x + 15 = 0 \\ x1x2 = 15 \\ x1 + x2 = - 8 \\ \\ x1 = - 5 \\ x2 = - 3[/tex]