1) x^2+5x+6=(x+2)(x+3)
D=25-24=1
X1=-5+1/2=-2
X2=-5-1/2=-3
2) x^2-5x+6=(x-3)(x-2)
D=25-24=1
X1=5+1/2=3
X2=5-1/2=2
3)x^2-8x+15=(x-5)(x-3)
D=64-60=4=2
X1=8+2/2=5
X2=8-2/2=3
4)x^2-7x+12=(x-4)(x-3)
D=49-48=1
X1=7+1/2=4
X2=7-1/2=3
5)x^2-x-12=(x-4)(x+3)
D=1+48=49=7
X1=1+7/2=4
X2=1-7/2=-3
6)x^2-3x-4=(x-4)(x+1)
D=9+16=25=5
X1=3+5/2=4
X2=3-5/2=-1