1'x^2-y^2-z^2-2yz=2'已知a,b,c是△ABC的3边,请判断并证明:a^2-b^2+c^2-2ac的正负性.3'请认真观察多项式:(x+1)(x+2)(x+3)(x+4)+1的特点,试判断并证明其是否是一个完全平方式.(请答题者写出理由,要让我懂```哈

f(x,y,z)=yz+xz使得,y^2+z^2=1,yz=3,求f最大值 若|x-3|+|y+2|+|2z+1|=0,求(xy-yz)(y-x+z) 因式分解 (x+y+z)^2+yz(y+z)+xyz (2X+Z-Y)/(X^2-XY+XZ-YZ)-(Y-Z)/(X^2-XY-XZ+YZ) 分式题:xy=x+y,yz=2(y+z),zx=3(z+x),求xyz/(xy+yz+xz)xy=x+y,yz=2(y+z),zx=3(z+x),求xyz/(xy+yz+xz) 求证不等式 xyz[yz(y+z)+zx(z+x)+xy(x+y)]>=2(xy+yz+xz)^2 (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=? 设x,y,z∈R+,xy+yz+xz=1,证明不等式:(xy)^2/z+(xz)^2/y+(yz)^2/x+6xyz≥x+y+zRt 化简(2x-y-z/x^2-xy-xz+yz)+(2y-x-z/y^2-xy-yz+xz)+(2x-x-y/z^2-xz-yz+xy) 若|x-3|+|y+z|+|2z+1|=0,求XY-YZ的值 若｜x-3｜+｜y+z｜+｜2z+1｜=0,求xy-yz的值 化简x^2-yz/[x^2-(y+z)x+yz]+y^2-zx/[y^2-(z+x)y+zx]+z^2-xy/[z^2-(x+y)z+xy] 因式分解x²-y²-z²=2yz+2x+1x²-y²-z²=2yz+2x+1因式分解 以知1/x=3/y=5/z,求4x^2+2yz+z^2/x+y-z＊x-z-y/8x^2+4yz+2z^2的值. 若f(x)=lg((1+x)/(1-x)),若f((y+z)/(1+yz))=1,f((y-z)/1-yz))=2,其中,-1 已知xy∶yz∶z x=3∶2∶1,求①x∶y∶z ②x/yz：y/zx 已知xy/x+y=3,yz/y+z=2,zx/z+x=1,求y的值