2(x+y)-(x-3y)=13 4（x+y）+3（x-3y)=1解方程组 2(x+y)-(x-3y)=13 4（x+y）+3（x-3y)=1
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2(x+y)-(x-3y)=134（x+y）+3（x-3y)=1解方程组2(x+y)-(x-3y)=134（x+y）+3（x-3y)=12(x+y)-(x-3y)=134（x+y）+3（x-3y)=1
2(x+y)-(x-3y)=13 4（x+y）+3（x-3y)=1解方程组 2(x+y)-(x-3y)=13 4（x+y）+3（x-3y)=1
2(x+y)-(x-3y)=13 4（x+y）+3（x-3y)=1
解方程组 2(x+y)-(x-3y)=13 4（x+y）+3（x-3y)=1
2(x+y)-(x-3y)=13 4（x+y）+3（x-3y)=1解方程组 2(x+y)-(x-3y)=13 4（x+y）+3（x-3y)=1
令a=x+y
b=x-3y
2a-b=13 (1)
4a+3b=1 (2)
(1)×3+(2)
6a+4a=39+1
a=4
b=2a-13=-5
所以
x+y=4
x-3y=-5
相减
4y=9
y=9/4
x=4-y=7/4
2x+2y-x+3y=13
x+5y=13....................1)
4x+4y+3x-9y=1
7x-5y=1....................2)
1)+2)得：
8x=14,x=7/4
代入1）：
5y=13-7/4=45/4
y=9/4
把式子化简，合并相同的项，第一个式子为x+5y=13,第二个式子为7x-5y=1
然后第一个式子乘以7，变为7x+35y=91.再和第二个式子相减。得到y=9/4,x=7/4
(x-y) (x-2y)+(x+2y) (x-3y)-2(x-3y) (x-4y)=
2（x+y)-3(x-y)=3 ,4(x+y)+3(x-y)=15
{3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1
x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20
{(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20
4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6
3(x+y)-2(x-y)=11 4(x+y)+3(x-y)=9
3(x+y)+2(x-y)=36 4(x+y)-5(x-y)=2
（x+y）/2- x-y/2=6 3(x+y)=4(x-y)
x+y/3+x-y/2=6 4(x+y)-2(x-y)=40
4(x-y)-3(x-y)=9 5(x-y)+2(x-y)=11
3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27
先化简再求值(x-y)(x-2y)+(x-2y)(x-3y)-2(x-3y)(x-4y) x=4 y=5
x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2
2(x+y)-(x-3y)=13 4（x+y）+3（x-3y)=1解方程组 2(x+y)-(x-3y)=13 4（x+y）+3（x-3y)=1
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