2、(1) 5x-3y+z=2.......(1)5x+2y-4z=3........(2)-5x+y-z=2..........(3)(1)+(3)：-2y=4y=-2..........(4)(1)-(2)：-5y+5z=-1z=(5y-1)/5........(5)(4)代入(5)：z=[5×(-2)-1]/5=-11/5........(6)把(4)(6)代入(1)：5x-3(-2)-11/5=2x=-9/25
