1) 5x^2+4x-1=0

2) 3x^2+10x+7=0

3) 28x^2-36x+11=0

1) 5 х^2+4 х-1=0

D=4^2-4*5 * (-1) = 16+20=36

x1,2 = (-4+-6) / 10

x1 = 1/5, x2=-1

2) 3x^2+10x+7=0

D=10^2-4*3*7=100-84=16

x1,2 = (-10+-4) / 9

x1=-2/3, x2=-14/9

3) 28x^2-36x+11=0

D = (-36) ^2-4*28*11=1296-1232=64

x1,2 = (36+-8) / 56

x1=11/14, x2=1/2