设有线性方程组(1+λ)x1+x2+x3=0x1+(1+λ)x2+x3=3x1+x2+(1+λ)x3=λ,问λ取何值时,此方程组:(1)有惟一解;(2)无解;(3)有无穷多个解?并在有无穷多解时求求通解.