Question

用代入法和加减法解方程用代入法解x+4y=-1,2x-3y=9用加减法解3x+4y=-1,x-2y=3

Answer 1

x+4y=-1

x=-4y-1

代入2x-3y=9

2(-4y-1)-3y=9

-8y-2-3y=9

11y=-11

y=-1

x=-4y-1=-4*(-1)-1=3

3x+4y=-1 (1)

x-2y=3 (2)

(1)+(2)*2

3x+4y-2x-4y=-1+6

x=5

y=(x-3)/2=1