3（y-z）^2-(2y+z)(-z+2y)这道题我是这样做的：3（y-z）^2-(2y+z)(-z+2y)=3（y-z)^2+(-z-2y)(-z+2y)=3(y-z)^2+z^2-4y^2=3(y^2-2yz+z^2)+z^2-4y^2=3y^2-6yz+3z^2+z^2-4y^2=4z^2-6yz-y^2(a+b-c)^2=[(a+b)-c]^2=(a+b)^2-2(a+b)c+c^2=a^2+b^2-2a+2bc+c^2

求Y(Z)=Z(Z+2)/(3Z-7)(Z+1)的z反变换 3（y-z）的2次方-（2y-z）（-z+2y） 3(y-2)^2-(2y+z)(-z+2y) 试证明(x+y-2z)+(y+z-2x)+(z+x-2y)=3(x+y-2z)(y+z-2x)(z+x-2y) 因式分解3(y-z)的平方-(2y+z)(2y-z)因式分解3(y-z)^2-(2y+z)(-z+2y) 已知(x+y)(x+z)=x,(y+z)(y+x)=2y,(z+x)(z+y)=3z,求x,y,z 2(x+y)(x+y-z)+3(y-z)(x+y-z) (x-3y+2z)(x+3y-2z) （x-2y+3z)(x+2y-3z) (2y-x-3z)(-x-2y-3z) （x-2y+z）（-x+2y+z） x+2y-z）（x+2y-z） （x+2y-z）(x-2y+z) 求化简(x+3y+2z)(x-3y+6z)(x+3y+4z-2z)(x-3y+4z+2z) 化简(y-x)(z-x)/(x-2y+z)(x+y-2z)+（z-y)(x-y)/(x-2z+y)(y+z-2x)+(x-z)(y-z)/(y+z-2x)(x-2y+z) 计算:(y-x)(z-x)/(x-2y+z)(x+y-2z)+(z-y)(x-y)/(x+y-2z)(y+z-2x)+(x-z)(y-z)/(y+z-2x)(x-2y+z) 2(x+y-z)-3(x-y+z)-5(x+y-z)+6(x-y+z) 计算 证明 ：x/(y+z)+y/(z+x)+z/(x+y)>=3/2其中 x,y,z>0