4x+5y=98 5y-4x=2 这可是二元一次方程哦!

4x+5y=98 5y-4x=2 这可是二元一次方程哦! 已知x,y∈R+,且1/x+4/y=1,求x+y的最小值x+y=x+x分之一+y+y分之4-1≥2+4-1=5,可是答案是9,为什么会错呢 x*x+2x+y*y-4y+5=0 x= y= 3(x+y)+2(x-y)=36 4(x+y)-5(x-y)=2 4(x-y)-3(x-y)=9 5(x-y)+2(x-y)=11 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 先化简再求值(x-y)(x-2y)+(x-2y)(x-3y)-2(x-3y)(x-4y) x=4 y=5 若(x*x+y*y)(x*x+y*y)-4x*x*y*y=0,求代数式(x*x+5xy+y*y)/(x*x+2xy+y*y)的值 已知x*x+4x+y*y-2y+5=0,则x*x+y*y=? 5x-4y(y-x)=? 化简[(3x+4y)^2-(2x+y)(2x-y)+(-x+y)(5x-y)]除以-2y,其中x=-1,y=1 化简求值：2(x+y)(x-2y)-2x(x+y),其中x、y满足x^2+y^2-2x+4y=-5 (4x-2y-z)-{5x[8y-2y-(x+y)]-x+(3y-10z)]=? kuaihuajian 3X=5Y （X+Y)*3X=(2Y+X)*4+2*2 x*x+y*y-2x+4y+5=0求x, 2x+y=4 x+2y=5 x+y等于?2x+y=4x+2y=5x+y等于? X^4-5X^2+4Y^4怎么变化成(X+Y)(X-Y)(X+2Y)(X-2Y)这步?就算是把(X+Y)(X-Y)(X+2Y)(X-2Y)算出来 也是=（X^2-Y^2)(X^2-4Y^2)=X^4-5X^2Y^2+4Y^4...也不是=(X^4-5X^2+4Y^4) 已知X.x+y.y-4x+2y+5=0,求4X.X-12X Y+9Y.y的值