13.求解下列齐次线性方程组:-|||-(1) ) (x)_(1)+(x)_(2)+2(x)_(3)-(x)_(4)=0, 2(x)_(1)+(x)_(2)+(x)_(3)-(x)_(4)=0, 2(x)_(1)+2(x)_(2)+(x)_(3)+ .-|||-=-|||-(2) ) (x)_(1)+2(x)_(2)+(x)_(3)-(x)_(4)=0, 3(x)_(1)+6(x)_(2)-(x)_(3)-3(x)_(4)=0, 5(x)_(1)+10(x)_(2)+(x)_( .-|||-:-|||-(3) { ) 2(x)_(1)+3(x)_(2)-(x)_(3)-7(x)_(4)=0, 3(x)_(1)+(x)_(2)+2(x)_(3)-7(x)_(3)=0, 4(x)_(1)+(x)_(2)-3(x)_ .-|||-=-|||-(4) ) 3(x)_(1)+4(x)_(2)-5(x)_(3)+7(x)_(3)=0, 2(x)_(1)-3(x)_(2)+3(x)_(3)-2(x)_(3)=0, 4(x)_(1)+11(x)_(2)-1 .-|||-,