Question

求大神解方程，感谢！！

Answer 1

(a)

x+2y+5=0 (1)
3x-y+1=0 (2)
(1)+2(2)
7x+7=0
x=-1
from (1)
x+2y+5=0
-1+2y+5=0
y=-2
(x,y)=(-1,-2)
(b)
y= -(3/4)x+2 (1)
y=(4/5)x- 1/2 (2)
(1)=(2)
-(3/4)x+2 =(4/5)x- 1/2
20[-(3/4)x+2] =20[(4/5)x- 1/2]
-15x+40=16x-10
31x=50
x=50/31
from (1)
y= -(3/4)x+2
=-(3/4)(50/31)+2
=-75/62 +2
=49/62
(x,y) = (50/31,49/62)
(c)
(x+1)/2 - (y-1)/3 =1
3(x+1) - 2(y-1) =6
/
3x-2y=1 (1)

(2x-1)/4 + (3y+2)/5 = -1

5(2x-1) + 4(3y+2) = -20
10x+12y = -23 (2)
6(1) +(2)
28x=-17
x= -17/28
from (1)
3x-2y=1
3(-17/28) -2y = 1
2y =-79/28
y= -79/56
(x,y) = ( -17/28 , -79/56)

追问

老师，第三个是不是做错了？

Answer 2

a:
x＝-1
y＝-2
后面的要自己解哦