Question

1.х^2-9х+14=0 2.х^2-11х+30=0 3.4х^2-20х+21=0 4.9х^2-12х-5=0

Answer 1

$x^{2} -9x+14=0$
$D=b^{2} - 4ac=(-9)^{2} - 4*1*14=81-56=25$
$\sqrt{D} = \sqrt{25} =5$
$x_{1}= \frac{9+5}{2} = \frac{14}{2} =7$
$x_{2} = \frac{9-5}{2} = \frac{4}{2} =2$
ответ:7;2.
$x^{2} -11x+30=0$
$D=b^{2} - 4ac=(-11)^{2} - 4*1*30=121-120=1$
$\sqrt{D} = \sqrt{1} =1$
$x_{1} = \frac{11+1}{2} = \frac{12}{2} = 6$
$x_{2} = \frac{11-1}{2} =\frac{10}{2}=5$
ответ:6;5
$4 x^{2} -20x+21=0$
$D=b^{2} -4ac=(-20)^{2} - 4*4*21=400-336=64$
$\sqrt{D} = \sqrt{64} =8$
$x_{1} = \frac{20+8}{8} = \frac{28}{8} =3,5$
$x_{2} = \frac{20-8}{8} = \frac{20}{8} =2,5$
ответ:3,5;2,5
$9 x^{2} -12x-5=0$
$D=b^{2} -4ac=(-12)^{2} - 4*9*(-5)=144+180=324$
$\sqrt{D}= \sqrt{324} =18$
$x_{1}= \frac{12+18}{18} = \frac{30}{18}$
$x_{2} = \frac{12-18}{18} = \frac{-6}{18} =[tex] \frac{-1}{3}$
ответ:$\frac{30}{18} ; \frac{-1}{3}$