shuraponomarev А) д=225-224=1
Х1=15+1/2=8
Х2=15-1/2=7
В)д=1+288=289=17
Х1=17-1/2=8
Х2=-1-17/2=-9
Г)д=9+72=81=9
Х1=3+9/2=6
Х2=3-9/2=-3

mashalisaeva А) x^2-15x+56=0
D=225-4*1*56=225-224=1
x1=15-1/2=7
x2=15+1/2=8

б) x^2+20x+21=0
D=400-4*1*21=400-84=316
x1=-20-17,7/2=-18,85
x2=-20+17,7/2=-1,15

в) x^2+x-72=0
D=1-4*1*(-72)=1+288=289
x1=-1-17/2=-9
x2=-1+17/2=8

г) x^2-3x-18=0
D=9-4*1*(-18)=9+72=81
x1=3-9/2=-3
x2=3+9/2=6