已知线性方程组:x1+x2+x3+x4+x5=a,3x1+2x2+x3+x4-3x5=0,x2+2x3+2x4+6x5=b,5x1+4x2+3x3+3x4-x5=2.求当a,b

:x1+x2+x3+x4+x5=a,① 3x1+2x2+x3+x4-3x5=0,② x2+2x3+2x4+6x5=b,③ 5x1+4x2+3x3+3x4-x5=2④ 先消去x1,①*3-②，x2+2x3+2x4+6x5=3a, ①*5-④，x2+2x3+2x4+6x5=5a-2, ∴方程组有解时5a-2=3a,a=1.由③，b=3. (2)x3=m,x4=n,x5=p,其中m,n,p是任意数， 由③，x2=3-2m-2n-6p, 代入①，x1=m+n+5p-2.