x y=五二x-y=4则x=多少y=多少-搜答案-百度作业网

原式=（x+2y)^2-（x+2y）+1/4=0则x+2y=1/2

x等于0y等于2.5xy等于0..

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

记u=x+y,v=x-y则解得：x=(u+v)/2,y=(u-v)/2代入等式得：f(u,v)=(u+v)^2/4-(u+v)/2*(u-v)/2即f(u,v)=(u^2+v^2+2uv)/4-(u^

x²-2xy+y²=(x-y)²=2²=4x³y-2x²y²+xy³=xy(x²-2xy+y²)=x

(1)×7+(2)×328y+27y=55xy所以y=0或x=1分别代入所以x=0.y=0x=1,y=1/2

4xy=(x+y)^2-(x-y)^2xy=〔(x+y)^2-(x-y)^2〕÷4运用这个,在进行计算.

2(x+xy)-[(xy-3y)-x]-(-xy)=2x+2xy-xy+3y+x+xy=3x+3y+2xy=3（x+y）+2xy=3*（-2）+2*3=0

3x²-xy+y²=101-xy+4y²=421-2得3x²-3y²=6x²-y²=2选B

这两题并不难证,我已做成图片,见下图（图片点击放大,如果没看到说明还在审核）

已知xy满足x²+y²+5/4(四分之五)=2x+y,求代数式(x+y)xyx²+y²+5/4=2x+yx²-2x+1+y²-y+1/4=0

∵x-y=4xy，∴2x+3xy-2yx-2xy-y=2(x-y)+3xyx-y-2xy=8xy+3xy4xy-2xy=112．故答案为：112．

x²-y²=(2-xy)-(1-xy)=1

xy/(x+y)=2(x+y)/xy=1/21/x+1/y=1/2(3x-xy+3y)/(-x+3xy-y)=(3/y-1+3/x)/(-1/y+3-1/x)=[3(1/x+1/y)-1]/[(3-(

求xy的最大值就是求4xy的最大值就是求x.(4y)的最大值.记z=4y,原方程写做x+z+5=(xz)/4.所以xz=4(x+z+5).也就是说,x和z是下面这个方程的根：a^2-b.a+4(b+5

∵X+Y=3,∴（X+Y)^2=9,即X^2+2XY+Y^2=9,∵x^2+y^2-3xy=4∴XY=1（以上两式相减）∴X^2+Y^2=7∵x^3y+xy^3=XY（X^2+Y^2）=1*7=7（因

把括号打开7X+4Y+XY-5Y-6X+6XY=X-Y+7XY=5+7*(-3)=-16

(7x+4y+xy)-6(六分之五y+x-xy)=7x+4y+xy-5y-6x+6xy=x-y+10xy把x-y=5和-xy=3代入x-y+10xy=5+10*(-3)=5-30=-25所以原式的值是

∵x=2,y=3∴2(xy^2+3y^3-x^2y)-(-2x^2y+y^3+xy^2)-4y^3=2xy²+6y³-2x²y+2x²y-y³-xy&

是不是打错了?应该是x²+y²-3xy吧?（x+y）²=x²+2xy+y²=9①x²+y²-3xy=4②①-②得:x²+