求指导本题解题过程，谢谢您！ ) (x)_(1)+(x)_(2)+2(x)_(3)=a 3(x)_(1)-(x)_(2)-6(x)_(3)=a+2 (x)_(1)+4(x)_(2)+11(x)_(3)=a+3 .-|||-已知线性方程组 有无穷多-|||-解,则 a= __-|||-第1空:-|||-__

求指导本题解题过程，谢谢您！