130 * 223% = 130 * 223/100 = 289,9
5,4 : 45% = 5,4 : 45/100 = 12
2х/5 = 7/9
2х * 9 = 7 * 5
18х = 35
х = 35 : 18
х = 1 17/18
____________________
5х - (х + 3) = 5
5х - х - 3 = 5
4х = 5 + 3
4х = 8
х = 8 : 4
х = 2
______________________
2х² = 0
х = 0
_________________________
х² - 8х + 7 = 0
D = (-8)² - 4 * 1 * 7 = 36
8 - √36
x₁ = ------------------ = 1
2 * 1
8 + √36
x₂ = ---------------------- = 7
2 * 1