D=64-4*12=16
x1=(-8+4)/2=-2
x2=(-8-4)/2-6
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6 6/13=84/13
84/13:(11+17)=3/13
(3/13)*11=33/13
(3/13)*17=51/13
33/13=2 7/13
51/13=3 12/13
=3*0+2*0+3*-1-3*-1=-3+3=0