3.设 ) (2-lambda )(x)_(1)+2(x)_(2)-2(x)_(3)=1 2(x)_(1)+(5-lambda )(x)_(2)-4(x)_(3)=2 -2(x)_(1)-4(x)_(2)+(5-lambda )(x)_(3)= . ,问λ为何值时,此方程组有唯一解、无解或有无-|||-穷多解?并在有无穷多解时求其通解.