4x^2 - 20 = 0

4x^2 = 20

x^2 = 20/4 = 5

x = +-корень(5)

2x - 8x^2 = 0

x - 4x^2 = 0

x(1-4x) = 0

x1 = 0   x2 = 1/4

2x^2 - 7x + 6 = 0

D = 49 - 4*2*6 = 1

x1 = (7 + 1)/4 = 2   x2 = (7 - 1)/4 = 3/2 = 1_1/2

x^2 - x = 2x - 5

x^2 - 3x + 5 = 0

D = 9 - 4*5 < 0 нет действительных корней...

Verified answer