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3y 4m

1、 2x+3y=3m+7(1) x-y=4m+7(2) 由(2)x3+(1)得5x=15m+28,得x=3m+ 28/5 由(2)x2-(1)得-5y=5m+7,即y=-m- 7/5 2、 x+y =3m+ 28/5+-m- 7/5 =2m + 21/5=6 即2m = 9/5 得m=9/10

1)5X+3Y=4M 这式子乘以4,得:20X+12Y=16M 4X-5Y=8M-3 这式子乘以5,得:20X-25Y=40M-15 得出的两个式子相减,得37Y=-24M+15 2)6X-2Y=9M 这式子乘以4,得:24X-8Y=36M 4X-5Y=8M-3 这式子乘以6,得:24X-30Y=48M-18 得出的两个式子相减,得22Y=...

9x+13y=-1 14x+10y=11 92x=153 X=153/92

D,Dx是什么鬼

解方程组2x?3y=11?4m3x+2y=21?5m得x=85?23m13y=18+4m26把x,y代入二元一次方程x+3y+7m=20得85?23m13+3(18+4m)26+7m=20解得m=2故选C.

直线与2x-3y=5平行,k=2m2+m?3m?m2=23,解得m=?98,满足2m2+m?32=m2?m?3≠ 4m?15,所以m=?98时两条直线平行.故选C.

4m-7n-2(m-2n) =4m-7n-2m+4n =4m-2m+4n-7n =2m-3n -(x²-2xy-y²)+(5x²-2xy-3y²) =-x²+2xy+y²+5x²-2xy-3y² =-x²+5x²+2xy-2xy-3y²+y² =4x²-2y²

3a²-7a-6=(3a+2)(a-3) 6x²-11xy+3y² =(3x-y)(2x-3y) 4m²+8mn+3n² =(2m+3n)(2m+n) 10x²-21xy+2y²=(10x-y)(x-2y)

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