x^2-4xy+4y^2-9z^2

x^2-4xy+4y^2-9z^2 二元函数Z=x^2-xy+4y^2,求二阶偏导数Zxx Zxy Zyy 已知实数x,y,z满足x=6-y,z^2-4z+4=xy-9,求x,y,z的值 已知实数x,y,z满足x=6-y,z^2-4z+4=xy-9,求x,y,z的值. 已知XY=2(X+Y),YZ=4(Y+Z),ZX=5(Z+X),求X,Y,Z已知XY=2(X+Y),YZ=4(Y+Z),ZX=5(Z+X),求X,Y,Z 方程组xy/x+y=2 yz/y+z=4 zx/x+z=5 求x,y,z x^2+y^2-2x+4y最小值为z,则（xy）^z= 若x,y,z满足x2+2y2+z2≤2xy-2y+4Z,求x,y,z 2x²y·(-4xy³z)计算 12xy(2x+3y+4z)因式分解 x²-y²+5x+3y+4（x+y-2xy)(x+y-z)+(xy-1）² 化简2y-3z/2yz+2z-3x/3zx+9x-4y/6xy 若x/3=y=z/4,且xy+xz+yz=76,求2x*x+12y*y+9z*z的值 (x+y-xy)/(x+y+2xy)=(y+z-2yz)/(y+z+3yz)=(z+x-3zx)/(z+x+4zx),且2/x=3/y=1/z,则xyz=? 已知（x+y-xy）/(x+y+2xy)=(y+z-2yz)/(y+z+3yz)=(z+x-3zx)/(z+x+4zx),且2/x=3/y-1/z,则xyz=? 解下(a+2)(a-2)(a^4+4a^2+16) (x^2+2xy+y^2)(x^2-xy+y^2)^22 (x+y+z)(-x+y+z)(x-y+z)(x+y-z) 设正实数x,y,z满足x^2-3xy+4y^2-z=0,则z/xy取得最大值时,x+2y+-z的最大值为 (A)0 (B) 9/8 (C)2 (D) 9/4 已知4x-3y=6z 2x+4y=14z 求2xy/x^+y^