求方程组x=eu usinv,y=eu-ucosv u对x和u对y的偏导数-搜答案-智慧作业帮

3x+2y=21①2x-5y=-11②①*2得6x+4y=42③②*3得6x-15y=-33④③-④得19y=42+3319y=75y=75/19代入①得3x+2*75/19=213x=21-150/

（4x+3y）-(3x+4y)=x-y=-10(4x+3y)+(3x+4y)=7x+7y=42除以7得x+y=6

由3x+4y=10得3x=10-4y所以x=10-4y/3再把这个代入4x+3y=6中,即；40-8y/3+3y=6两边同乘3即：40-8y+9y=18求得y=-12再把y=-12代入x=10-4y/

|x-2|=7-|y-5|≥0解得4≤y≤12|x-2|=y-6≥0解得y≥6则,6≤y≤12|x-2|=7-|y-5|,|x-2|=y-6则,7-|y-5|=y-67-y+5=y-62y=18解得y

3x+4y=16①5x-6y=33②①x5得15x+20y=80③②x3得15x-18y=99④③-④得38y=-19得y=-1/2把y=-1/2代入①得x=6

xy/(2x+y)-xy/(2x-y)=3xy/(2x-y)+xy/(2x+y)=4；一、两公式对加得2xy/(2x+y)=7xy=(2x+y)*7/2二、把xy代入原公式求解就行了：(2x+y)*7

10％x+15％y=12.42左右同乘100,就是10x+15y=1242x+y=698,则y=698-x,代入上式10x+15（698-x）=1242解得x=2069.6y=698-x=698-20

把Y=3X+1代入x+2y=9解得X=1,Y=4

x+y/3+x-y/2=63(x+y)-2(x-y)=282x+2y+3x-3y=363x+3y-2x+2y=285x-y=36x+5y=285x-y=365x+25y=14026y=104y=4x=

解y+5=3(x-1)y=3x-8代入5(y-1)=3(x+5)5(3x-8-1)=3(x+5)15x-45=3x+1512x=-60x=-5y=3x-8=-23再问：喂、你好像做错了、再看看啊..再

解:7x-3y=0.(1)2x-y=1.(2)由(2)得y=2x-1把y=2x-1代入(1)得7x-3(2x-1)=07x-6x+3=0x=-3y=2x-1=2×(-3)-1=-7所以x=-3,y=-

5X+3Y=181式7X-6Y=152式1式×2+2式(10x+6y)+(7x-6y)=36+1517x=51X=3把X=3带入1式15+3y=18y=1方程组的解为X=3y=1注意大括号

设x/2=y/3=z/4＝K则x=2Ky=3Kz=4K原方程就变成2K+3K+4K=18所以K=2则x=4y=6z=8

用加减消元法,2x-2y=1所以X-y二2分之1

2x+y=6x+2y=9相加得3x+3y=15x+y=5相减得2x+y-x-2y=6-9x-y=-3

2x（2x-5y）=16x24x+3y=584x-10y=324x-4x-10y-3y=32-58-13y=-26Y=2X=13

X=-3/4y=2

{2x+y=6①{x-3y=1②①减②得x+4y=57y(x-3y)²-(3y-x)³=7y(x-3y)²+(x-3y)³=7y(x-3y)²+(x-

7Y(X-3Y)^2-(3Y-X)^3=7Y(X-3Y)^2+(X-3Y)^3=(X-3Y)^2(7Y+X-3y)=(X-3Y)^2(X+4Y)因为X-3Y=1所以上式=(X-3Y)^2(X+4Y+X