4x y=5 2x-2y=1和ax by=3 ax-by=1

四个方程标好号(3)×3-(1)得x=4把x=4代入(3)得∴4-y=1∴y=3把x=4,y=3分别代入(2)(4)得4a+3b=1(5)4b+3a=6(6)解这个方程组得a=-2b=3∴(a+b)的

1.2(Xy+Xy)-3(Xy-xy)-4Xy=2*2xy-0-4xy=4xy-4xy=02.1/2ab-5aC-(3acb)+(3aC-4aC)=1/2ab-5ac-3acb-ac=1/2ab-6a

因为x=1,y=-1,和x=3y=-5都是关于x,y的二元一次方程ax+by+2=0的解所以得到a-b+2=03a-5b+2=0所以解得a=-4b=-2所以原方程为-4x-2y+2=0将x=-4,y=

(-3x^y+2xy)-(4x^+xy)=-3x^y+2xy-4x^-xy=-3x^y+xy-4x^所以填上-3x^y+xy-4x^

(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)=-6xy+3x-3y=-6×(-2)+3×1=15

原式=3x-3y-6xy=3-12=-9

(x-xy)+(xy-y)=40-20x-xy+xy-y=20x-y=20(x-xy)-(xy-y)=40-(-20)x-xy-xy+y=60x+y-2xy=60

你看一下 我做的有点急 不知道对不

(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)=-2xy+2x+3y-3xy-2y+2x-x-4y-xy=-6xy+3x-3y=-6xy+3*(x-y)当时,原式=-6*1+3*

于x\y的方程组2x-3y=3,ax+by=-1和3x+2y=11,2ax+3by=3的解相同那么两个方程组的解都应该满足2x-3y=3和2x+2y=11两个方程.所以两个方程组的解就是方程组2x-3

1)=(1-x²)/(x²+1)²2)=2xsin²(3x+2)+3x²sin(6x+4)3)=题目实在看不懂4）(logae/3x)*cos&sup

(ax²-2xy+y²)-(-ax²+bxy+2y²)=2ax²-(2+b)xy-y²=6x²-9xy+cy²故:2a=

2X-3Y=3---------（1）AX+BY=-1--------（2）和3X+2Y=11-------（3）2AX+3BY=3-------（4）的解相同,先解（1）,（3）得x=3y=1,代入

[3xy(1-x)-6xy(x-1/2)]*2x*(-xy)平方=(3xy-3x²y-6x²y+3xy)(2x³y²)=12x^4y³-18x^5y&

（-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)=(-2xy-3xy-xy)+(2x+2x-x)+(3y-2y-4y)=-6xy+3x-3y=-6+3*3=3

由于(ax²-2xy+y²)-(-ax²+bxy+2y²)=2ax²-(2+b)xy-y²=8x²-7xy-cy²；若欲

3x^2y-[2xy^2-4(1/2xy-3/4x^2y)+xy]+3xy^2=3x^2y-2xy^2+2xy-3x^2y-xy+3xy^2=xy^2+xy由x=3,y=-1/3得：原式=3*1/9-

(ax^2-2xy+y^2)-[-ax^2+bxy-(1/2)cy^2]=6x^2-5xy+cy^2ax²-2xy+y²+ax²-bxy+（1/2）cy²=6x

x-y=(x-xy)+(xy-y)=40+(-20)=20x+y-2xy=(x-xy)-(xy-y)=60

(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)=-2xy+2x+3y-3xy-2y+2x-x-4y-xy=-6xy+3x-3y=-6*(-2)+3*1=15不懂可追问,有帮助请采