Question

Решите и запишите подробно решение прошу!
ТОЛЬКО 3, 4 НОМЕР 9.8(нижний)

Answer 1

#9.8
3)
$(2x-7)*(x+5)=0$
$2x^{2}+10x-7x-35=0$
$2x^{2}+3x-35=0$
$D=b^{2}-4ac=3^{2}-4*2*(-35)=9+280=289$
$x_{1}=frac{-b+sqrt{D}}{2a}=frac{-10+sqrt{289}}{2*2}=frac{-10+17}{4}=frac{7}{4}=1,75$
$x_{2}=frac{-b-sqrt{D}}{2a}=frac{-10-sqrt{289}}{2*2}=frac{-10-17}{4}=frac{-27}{4}=-6,75$

4)
$(x-4)*(5x+1)=0$
$5x^{2}+x-20x-4=0$
$5x^{2}-19x-4=0$
$D=b^{2}-4ac=-19^{2}-4*5*(-4)=361+80=441$
$x_{1}=frac{-b+sqrt{D}}{2a}=frac{-(-19)+sqrt{441}}{2*5}=frac{19+21}{10}=frac{40}{10}=4$
$x_{2}=frac{-b-sqrt{D}}{2a}=frac{-(-19)-sqrt{441}}{2*5}=frac{19-21}{10}=frac{-2}{10}=-0,2$