Question

用代入法,加减消元法解下列方程2x+3y=19x+5y=1

Answer 1

2x+3y=19 (1)

x+5y=1 (2)

代入法

由(2)得x=1-5y

代入(1)

2(1-5y)+3y=19

2-10y+3y=19

2-7y=19

y=-17/7

x=1-5y=92/7

加减法

(1)-2*(2)

2x+3y-2(x+5y)=19-2*1

2x+3y-2x-10y=17

-7y=17

y=-17/7

(1)*5-(2)*3

5(2x+3y)-3(x+5y)=19*5-1*3

10x+15y-3x-15y=92

7x=92

x=92/7