用消元法解下列线性方程组:-|||- x1+3x2+5x3-4x4 =1, x1+3x2+2x3-2x4+x5=-1, x1-2x2+x3-x4-x5=3, x1-4x2+x3+x4-x5=3, x1+2x2+x3-x4+x5=-1;