a+b+c=1①4a+2b+c=2②9a+3b+c=1③(2)-(1)得 3a+b=1(4)(3)-(2) 5a+b=-1(5)(5)-(4)得 a=-1把a=-1代入（4）得b=4把a=-1,b=4代入（1）得c=-2∴a=-1 b=4 c=-2...