Смотри.....................
-3x^2 - 7x + 6 = 0 | * (-1)
3x^2 - 7x - 6 = 0
D = 49 + 4*3*6 =121 = 11
7 + 11/ 6 = 3
7 - 11/6 = 0.6
#1
-2х + 8 + 4х - 8 = 0
2х = 0
х = 0
#2
3у - 18 - 12у + 18 = 18
-9у = 18
у = -2
#3
х + х + 1.5 + х + 2 = 23
3х = 23 - 1.5 - 2
3х = 19.5
х = 6,5
По т. Виета
х1+х2= -р
х1*х2=q
1)
x1=-6, x2= -2
p=8
q=12
x²+6x+12=0
2)
x1= -6, x2=7
p=-1
q= -42
x² -x -42=0