Суравнением 1. -3(х-2.1)=0 2. (х-1.8)*(х+5)=0 3. (7.2-х)*(2х+4)=0

1. -3х + 6.3 = 0
-3х = -6.3
х = 2.1
ответ: 2.1

2. х^2 + 5х - 1.8х - 9 = 0
х^2 + 3.2х - 9 = 0
D = 10.24 + 36 = 46.24
x1 = (-3.2 + 6.8)/2 = 3.6/2 = 1.8
x2 = (-3.2 - 6.8)/2 = -5
ответ: -5;1.8

3. 14.4х + 28.8 - 2х^2 - 4х = 0
-2х^2 + 10.4х + 28.8 = 0
х^2 - 5.2х - 14.4 = 0
D = 27.04 + 57.6 = 84.64
x1 = (5.2 + 9.2)/2 = 14.4/2 = 7.2
x2 = (5.2 - 9.2)/2 = -2
ответ: -2;7.2