f(x,y)=x*x*x+y*y*y-9xy+27极值
问题描述：
f(x,y)=x*x*x+y*y*y-9xy+27极值
答
fx(x,y)=3x^2-9yfy(x,y)=3y^2-9x当fx(x,y)=0,fy(x,y)=0时,解得：x=0,y=0；或x=3,y=3fxx(x,y)=A=6xfxy(x,y)=B=-9fyy(x,y)=C=6y当x=0,y=0时,AC-B^20,AC-B^2>0所以为极小值点,代入有：f(3,3)=0所以函数在(3,3)处有极小...