1)X^2-6X+8=0
2)X^2+2X-8=0
3)X^2-2X-8=0
4)X^2+6X+8=0

1) D=(-6)^2-4×1×8=36-32=4
X1=6+2/2=4
X2=6-2/2=2
2) D=2^2-4×1×(-8)=4+32=36
X1= -2+6/2=2
X2= -2-6/2=-4
3) D= (-2)^2-4×1×(-8)=4+32=36
X1= 2+6/2=4
X2= 2-6/2= -2
4) D= 6^2-4×1×8= 36-32 = 4
X1= -6+2/2=-2
X2 = -6-2/2=-4