х^2-9 х+14=0

x^2-11 х+30=0

4x^2-20 х+21=0

9x^2 - 12 х-5=0

х^2-9 х+14=0

D=b^2-4ac = (-9) ^2-4*1*14=81-56=25

VD=V25=5

x1 = 9+5/2*1=14/2=7

x2 = 9-5/2=4/2=2

x^2-11 х+30=0

D = (-11) ^2-4*1*30=121-120=1

VD=V1=1

x1=11+1/2=12/2=6

x2 = 11-1/2=10/2=5

4x^2-20 х+21=0

D = (-20) ^2-4*4*21=400-336=64

VD=V64=8

x1=20+8/2*4 = 28/8 = 3,5

x2 = 20-8/2*4=12/8 = 1,5

9x^2 - 12 х-5=0

d = (-12) ^2-4*9 * (-5) = 144+180=324

VD=V324=18

x1=12+18/2*9=30/18 = 1 12/18

x2=12-18/2*9=-6/9 = - 2/3