Помогите решить уравнения. 7x=2x. x2-25=0. x2+3x+2=0. x2-2x-9=0.

а). 7х = 2х
7х - 2х = 0
5х = 0
х = 0
б). х^2 - 25 = 0
х^2 = 25
х = sqrt 25
х1 = 5
х2 = -5
в). х^2 + 3х + 2 = 0
D = b^2 - 4ас = 9 - 4*2 = 1
х1 = (-b + sqrt D)/2а =
(-3 + 1)/2 = -2/2 = -1
х2 = (-b - sqrt D)/2а =
(-3 - 1)/2 = -4/2 = -2
г). х^2 - 2х - 9 = 0
D = 4 + 4*9 = 40
х1 = (2 + sqrt 40)/2 =
(2 + 2sqrt 10)/2 = 1 + sqrt 10
х2 = (2 - sqrt 40)/2 =
(2 - 2sqrt 10)/2 = 1 - sqrt 10