Question

解方程组2A+2B-7C=1 2A-7B+2C=2 负7A+2B+2C=3

Answer 1

2A+2B-7C=1

2A-7B+2C=2

-7A+2B+2C=3

(2A+2B-7C)-(2A-7B+2C)=1-2

9B-9C=-1

7(2A-7B+2C)+2(-7A+2B+2C)=7*2-2*3

-45B+18C=20

45(9B-9C)+9(45B+18C)=45*(-1)+9*20

-243C=135

C=-5/9

9B-9(-5/9)=-1

B=-2/3

2A+2(-2/3)-7(-5/9)=1

A=-7/9

所以A=-7/9,B=-2/3,C=-5/9