Ср3.
1.
а) х²-3х+2=0
D= (-3)²-4*1*2=9-8=1
x1= (3+1)/2= 2, x2= (3-1)/2= 1.
б) х²+5х+7=0
D=5²-4*1*7=25-28= -3<0 => нет корней
2. х²-4х+1=0
D= (-4)²-4*1*1=16-4= 12
x1= (4+v12)/2= (4+2v3)/2= (2(2+v3)) /2= 2+v3
x2= (4-v12)/2= 2-v3
3. x²/(x+3)= 9/(x+3)
1) x+3≠0 при х≠ -3
2) х²= 9,
х1,2= ±v9
x1= 3, x2= -3
3) х1 =3, х2= -3, х≠ -3 => х= 3.