求解几个方程组1.5x+4y=-22.2x+3y=13.6x-6y=54.x=4y+2x+2y=43x+4y=2-3x+9y=-1x-2y=-2

Question

求解几个方程组
1.5x+4y=-2 2.2x+3y=1 3.6x-6y=5 4.x=4y+2
x+2y=4 3x+4y=2 -3x+9y=-1 x-2y=-2

Answer 1

1:5x+4y=-2,x+2y=4
x=4-2y,代入5x+4y=-2中,5(4-2y)+4y=-2,y=3,x=4-2y=-2
2:2x+3y=1,两边乘以3得6x+9y=3
3x+4y=2,两边乘以2得6x+8y=4,
两式相减y=-1,代入2x+3y=1,x=2
3:6x-6y=5,
-3x+9y=-1,两边乘以2得-6x+18y=-2
两式相加12y=3,y=1/4,代入6x-6y=5,x=13/12
4:x=4y+2代入x-2y=-2
4y+2-2y=-2,y=-2,x=4y+2=-6