3(x-y-1)=y-9,2分之x 3分之y=2-搜答案-搜搜考试网

原式=(9x²+24xy+16y²-4x²+y²-5x²+6xy-y²)÷(-2y)=(30xy+16y²)÷(-2y)=-15x

原式=x(1+2+3+……+9)+y(1+1/2+1/6+……+1/72)=45x+y(2-1/2+1/2-1/3+……+1/8-1/9)=45x+y(2-1/9),x=1,y=-9时原式=45-9（

由2(X+Y)3X+3Y=24得：2(X+Y)X+Y=8①;(X+Y/2X)XY/2Y=1得：X+Y=4②;由①、②得出Y=8(1-X),进入②知X=4/7；即Y=24/7

（1+2+3+...+9）x+(1+(1-1/2)+(1/2-1/3)+...+(1/7-1/8)+(1/8-1/9))y=50x+(1+1-1/9)y=100+270=370

郭敦顒回答：求y^n+3y'+2y=2x^2+x+1的通解3y′=2x^2+x+1－y^n－2y∴y′=（2x²+x+1－y^n－2y）（1）又y^n+3dy/dx+2y=2x^2+x+1∴

1.x=2y=7/32.x=-2y=-4

（4-x)(3x+6)=0-3(x-4)(x+2)=0x1=4,x2=-24y(y-1)=2y(y-1)4y(y-1)-2y(y-1)=02y(y-1)=0y1=0,y2=1

化简（x+y）+(2x+y/1*2)+(3x+y/2*3)+...+(9x+y/8*9),并求当x=2,y=9时的值（x+y）+(2x+y/1*2)+(3x+y/2*3)+...+(9x+y/8*9)

(7x-2y)(3x-2y-1)-(4x+3y)(9x+6y)=21x^2-14xy-7x-6xy+4y^2+2y-36x^2-24xy-27xy-18y^2=-15x^2-70xy-7x-14y^2

3x+2y=13①3x-2y=5②由①+②,得6x=18,x=3x=3代入②,得y=2该方程组的解集为x=3,y=2x-y/3=x+y/2+1①2x-5y=9②由①,得-y/3=y/2+1,y=-6/

解(x-y)(x+y)-(x-2y)²+x(3x-5y)-(x-y)(x-2y)=(x²-y²)-(x²-4xy+4y²)+(3x²-5xy

3(x+y)-4(x-y)=4(x+y)/2+(x-y)/6=1令a=x+y,b=x-y3a-4b=4(1)a/2+b/6=1则3a+b=6(2)(2)-(1)5b=2b=2/5a=(6-b)/3=2

4x=9yx=9/4*y(1)(x+y)/y=[(9/4)y+y]/y=(9/4+1)y/y=9/4+1=13/4(2)(y-x)/2x=[y-(9/4)y]/[2*(9/4)y]=(1-9/4)y/

x=-0.8;y=1

解9y=3x-(x-1)2x-9y+1=0①4(x+y)-(2x+4)=8y2x-4y-4=0②②-①得：5y-5=0∴y=1将y=1代入①得：2x-9+1=0∴x=4∴方程的解为：x=4,y=1

完整设1/(x+y)=a,1/(x-y)=b原方程组可变为4a+6b=39b-a=1a=9b-136b-4+6b=3b=1/6,a=1/2x+y=2x-y=6所以原方程组的解为：x=4,y=-2

把x=9y带入到3x=2y+1中得到3*(9y)=2y+127y=2y+125y=1y=1/25x=9y=9/25所以x=9/25,y=1/25

x+y=3则y=3-x带入x+2y=9解得x=-3,y=6剩下的都这样解

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