1)

4х² - 12х = 0

4х * (х - 3)

4х = 0    х - 3 = 0

х1 = 0     х2 = 3

2)

х*(х - 2) + 5*(х - 2) = 0,

(х - 2)*(х + 5) = 0,

х - 2 = 0     х + 5 = 0,

х1 = 2         х2 = - 5

3)

(2х - 3)(х + 7) = (х - 4)(2х + 3) + 3

2х² + 14х - 3х - 21 = 2х² + 3х - 8х - 12 + 3,

14х - 3х - 3х + 8х = -12 + 3 + 21,

16х = 12,

х = 12/16,

х = 3/4   (или  х = 0,75)