f(x,y)=x³-4x²+2xy-y²+5極値.

f(x,y)=x³-4x²+2xy-y²+5極値.

f'x=3x^2-8x+2y=0
f'y=2x-2y=0-->x=y,代入式:3x^2-6x=0,
x=0or2,y=0or2
A=f"xx=6x-8
C=f"yy=-2
B=f"xy=2
x=0,y=0,A=-2,B=2,C=-2,AC-B^2=-8*(-2)-4=12>0,A