Помогите с алгеброй

Решить уравнение:

1) 4 х^2-28 = 0;

2) 7x^2+9x = 0;

З) х^2+5 х-36=0;

4) 3 х^2-28 х+9 = 0;

5) 2 х^2-8 х+15 = 0;

6) 25x^2-10x+1 = O.

4 х^2-28=0

a=4

b=0

c = - 28

D=144 - 2k

x1 = 12/4=3

x2=-12/4 = - 3

7x^2+9x=0

a=7

b=9

c=0

D=81 - 2k

x1 = - 9+9/14 = 0

x2 = - 9-9/14 = 1 2/7

x^2+5x-36=0

a=1

b=5

c = - 36

D = 144 - 2k

x1 = - 5+11/2 = 3

x2 = - 5-11/2 = - 8

3x^2-28x+9=0

a=3

b = - 28

c=9

D=676 - 2k

x1 = 28+26/6 = 5 1/3

x2 = 28-26/6 = 1/3

2x^2-8x+15=0

a=2

b = - 8

c=15

D=-56 - 0k

25x^2 - 10x+1=0

a=25

b = - 10

c=1

D = 0 - 1k

x1 = 10/50 = 1/5