红色网孔:2i2+3(i2+i3+5)-i1=0
5i2+3i3-i1+15=0..........(1)
绿色网孔:2i2-4i3+10=0................(2)
A点:i1+2i3+i2+i3=0
i1+i2+3i3=0..............(3)
(1)-(3) 4i2-2i1+15=0........................(4)
(2)x3 - (3)x4 4i1+10i2+30=0..........(5)
(4)x2 + (5) 18i2+60=0,i2=-10/3 A。