已知方程组(I)
x1+ax2+x3+x4=22x1+x2+bx3+x4=42x1+2x2+3x3+cx4=1与(II)
x1+x2+x3+x4=1−x2+2x3−x4=2x3+2x4=−1同解,试确定a,b,c.