... x1=1,x2=2,x 3 =3) 7.x1+3x2− 2x 3 + x4+ x5=1,x1+3x2− x 3 +3x4+2x5 =3, x1+3x2− 3x 3 − x4=2.(DS. Hˆe.vˆo nghiˆe.m)8.5x1+ x2− 3x 3 = −6,2x1− 5x2+7x 3 =9,4x1+2x2− ... x2+3x 3 =3, 3x1+ x2− 5x 3 =0,4x1− x2+ x4 =3, x1+3x2− 13x 3 = −6.(DS. x1=1,x2=2,x 3 =1)27.2x1− x2+ x 3 − x4=1,2x1− x2− 3x4=2,3x1− x 3 + ... x2− 2x 3 − 3x4=8,3x1+2x2− x 3 +2x4=4,2x1− 3x2+2x 3 + x4= −8.(DS. x1=1,x2=2,x 3 = −1, x4= −2) 33 .x2− 3x 3 +4x4= −5,x1− 2x 3 +3x4= −4,3x1+2x2−...