Question

Помогите.плиз
x2 + 5x – 36 = 0
D =
x2 =
x1 + x2 =

x2 – 10x + 21 = 0
D =
x2 =
x1 + x2 =

x2 – 8x + 15 = 0
D =
x2 =
x1 + x2 =

Answer 1

$x^2 + 5x-36 = 0$

$D =b^2-4ac=5^2-4*1*(-36)=25+144=169$

$x_1 =\frac{-b+\sqrt{D} }{2a} =\frac{-5+13}{2} =\frac{8}{2} =4$

$x_2 =\frac{-b-\sqrt{D} }{2a} =\frac{-5-13}{2} =\frac{-18}{2} =-9$

$x_1 + x_2 =4+(-9)=-5$

$x^2-10x + 21 = 0$

$D =(-10)^2-4*1*21=100-84=16$

$x_1 =\frac{-b+\sqrt{D} }{2a} =\frac{10+4}{2} =\frac{14}{2} =7$

$x_2 =\frac{-b-\sqrt{D} }{2a} =\frac{10-4}{2} =\frac{6}{2} =3$

$x_1 + x_2 =3+7=10$

$x^2 -8x + 15 = 0$

$D =b^2-4ac=(-8)^2-4*1*15=64-60=4$

$x_1 =\frac{-b+\sqrt{D} }{2a} =\frac{8+2}{2} =\frac{10}{2} =5$

$x_1 =\frac{-b-\sqrt{D} }{2a} =\frac{8-2}{2} =\frac{6}{2} =3$

$x_1 + x_2 =5+3=8$