9.8. 1) -2x² + 5x - 17; 3) 2x² - 7x - 13; 5) -0,2x² + 7x - 18;

9.8. 1) $$-2x^2 + 5x - 17$$

$$-2(x^2-\frac{5}{2}x+\frac{17}{2})=-2(x^2-\frac{5}{2}x+\frac{25}{16}-\frac{25}{16}+\frac{17}{2})=-2((x-\frac{5}{4})^2+\frac{111}{16})$$

3) $$2x^2 - 7x - 13$$

$$2(x^2-\frac{7}{2}x-\frac{13}{2})=2(x^2-\frac{7}{2}x+\frac{49}{16}-\frac{49}{16}-\frac{13}{2})=2((x-\frac{7}{4})^2-\frac{153}{16})=2((x-\frac{7}{4})^2-(\frac{\sqrt{153}}{4})^2)=2(x-\frac{7}{4}-\frac{\sqrt{153}}{4})(x-\frac{7}{4}+\frac{\sqrt{153}}{4})$$

5) $$-0,2x^2 + 7x - 18$$

$$-0,2(x^2-35x+90)=-0,2(x^2-35x+\frac{1225}{4}-\frac{1225}{4}+90)=-0,2((x-\frac{35}{2})^2-\frac{865}{4})=-0,2((x-\frac{35}{2})^2-(\frac{\sqrt{865}}{2})^2)=-0,2(x-\frac{35}{2}-\frac{\sqrt{865}}{2})(x-\frac{35}{2}+\frac{\sqrt{865}}{2})$$

Ответ: 1) $$-2((x-\frac{5}{4})^2+\frac{111}{16})$$; 3) $$2(x-\frac{7}{4}-\frac{\sqrt{153}}{4})(x-\frac{7}{4}+\frac{\sqrt{153}}{4})$$; 5) $$-0,2(x-\frac{35}{2}-\frac{\sqrt{865}}{2})(x-\frac{35}{2}+\frac{\sqrt{865}}{2})$$