co nhieu cach lam nhung o day minh se lam cach la doan nghiem sau do chia da thuc cho da thuc x^4-x^3-2x-4 (1 ) nhan thây x=-1la nghiem cua (1) nen ta lay x^4-x^3-2x-4 chia cho x +1 ta duoc: x^3 -2x^2 +2x -4 =>x^4-x^3-2x-4= (x+1 )( x^3 -2x^2 +2x -4)(*) ta phan tich tiêp x^3 -2x^2 +2x -4 =( x^3 -2x^2) +(2x -4) =x^2(x -2) +2(x -2) =(x -2)(x^2 +2) the vao (*) ta dc: x^4-x^3-2x-4= (x+1 )(x -2)(x^2 +2) 1)thuc hien phep chia ta dc: 3x^3+13x^2-7x+5 =(3x-2)(x^2 +5x +1) +7/(3x -2) de thuong co gia tri nguyen thi: 3x -2 phai la uoc cua 7: 3x- 2 =1 =>x=1 3x-2=-1 =>x=1/3 3x-2=7=>x =3 3x -2 =-7=>x=5/3 2)thuc hien phep chia A (x) cho x +1 ta dc: a^2x^3+3ax^2-6x-2a =(x+1)[ a^2x^2 +(3a -a^2)x +( -6-3a +a^2)] + (-a^2 +a +6) de A(x) chia het cho x +1 thi: -a^2 +a + 6=0 <=> -(a^2 -a -6) =0 <=> a^2 -a -6 =0 <=>a^2 -2a +3a -6 =0 <=>(a^2 -2a) +(3a -6)=0 <=>a(a -2) +3(a -2)=0 <=>(a -2)(a +3)=0 => a -2 =0 hoac a +3 =0 =>a =2 hoac a=-3
