ax-by=m cx+dy=-n 解是x=-3 y=2
acx-bcy=cm
acx+ady=-an
y(ad+bc)=-an-cm
y=-(an+cm)/(ad+bc)=2,
adx-bdy=dm
bcx+bdy=-bn
x(ad+bc)=dm-bn
x=(dm-bn)/(ad+bc)=-3
ax-2by=4m -cx-2dy=4n
acx-2bcy=4cm
-acx-2ady=4an
-2y(bc+ad)=4(cm+an)
y=-2(cm+an)/(bc+ad)=-2*2=-4
adx-2bdy=4dm
-bcx-2bdy=4bn
x(ad+bc)=4(dm-bn)
x=4(dm-bn)/(ad+bc)=4*(-3)=-12.
∴ x=-12；y=-4.