Х^2-9х+14=0 x^2-11х+30=0 4x^2-20х+21=0 9x^2-12х-5=0

х^2-9х+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^2-11х+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^2-20х+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^2-12х-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