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