不解方程组2x-y =12 x 2y =11-搜答案-搜狗做题网

7y（x-3y）²-2（3y-x）³=（x-3y）²（7y-6y+2x）=（x-3y）²（y+2x）=1²x6=6

2x+3y=103x+2y=15,把两式相加得：5x+5y=25,x+y=5,把两式相减得：-x+y=-5,x-y=5,(x+y)(x-y)=5×5=25

7y(x-3y）的平方-2(3y-x)的立方=(x-3y)²（7y+2x-6y）=(x-3y)²（2x+y）x-3y=1.（1）x+4y=6.（2）（1）+（2）得2x+y=7则(

原式=2x2y+2xy-3x2y-3xy-4x2y=-5x2y-xy当x=-2，y=12时，原式=-9．

原式=4x2y-6xy+3（4xy-2）+x2y+1=5x2y+6xy-5当x=2，y=-12时，原式=5×4×（-12）+6×2×（-12）-5=-21．

x=5,y=-22x+y=10-2=83x-19=15-19=-4=2×(-2)所以x=5,y=-2是方程组的解

把x=5,y=-2代入2x+y=8,3x-19=2y,方程成立.是解!

（X+Y）2=1402X2Y*3=14400（X+Y）2=140→X+Y=70→Y=70-X①2X2Y*3=14400→XY=1200②把①代人②得：X（70-X）=1200X²-70X+1

7y(x-3y)²-2(3y-x)³=7y(x-3y)²+2(x-3y)³=(x-3y)²[7y+2(x-3y)]=(x-3y)²(2x+y

3x+4y=104x+3y=-2两式相加7x+7y=87(x+y)=8x+y=8/7

解方程组得到{x=16/7y=3/7∴7y(x-3y)=3×(16/7-9/7)=3

2X+Y=6,X-3Y=1解得:y=4/77Y(X-3Y)^2-2(3Y-X)^3=7y*1^2-2*(-1)^3=7y+2=7*4/7+2=6

x2y+xy2=xy*(x+y)因为x+y=-(7+xy)又x+y=（9+2xy)\3所以（9+2xy)\3=-(7+xy)3+2xy\3=-7-xy5xy\3=-10解得xy=-6所以x+y=-(7

1.2*(2007x-2008y)=4014x-4016y=4018(4014x-4016y)+3(x+y)+4018=4017x-4013y+4018=4018+3+4018=80392.3*(x-

2x+3y=3①,2x+y=5②由①+②得4x+4y=8即x+y=2

(2x-y)^3-(2x-y)^2(x-3y)=(2x-y)^2*(2x-y-x+3y)=(2x-y)^2*(x+2y)=12^2*11=1584

如果x,y符号相反,绝对值相等,即y=-x,代入原方程组,得3x-2x=m+1,4x-2x=m-1,即x=m+1,2x=m-1解之,2(m+1)=m-1,得m=-3如果x比y大1,即x=y+1,代入原

{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

7y(x-3y)^2-2(3y-x)^3=7y(x-3y)^2+2(x-3y)^3=(x-3y)^2[7y+2(x-3y)]=(x-3y)^2(2x+y)把2x+y=-6,x-3y=4,代入,原式=(