f'x=-4x-8y-13=0,即4x+8y=-13
f'y=-20y-8x-31=0,即4x+10y=-31/2
解得极值点:
x=-3/4
y=-5/4
f"xx=-4,f"yy=-20,f"xy=-8
4*20-8^2=80-64=16>0.因此有极值,且为极大值,其值
f(-3/4,-5/4)=1-2*9/16-10*25/16-8*15/16+13*3/4+31*5/4=(16-18-250-120+156+620)/16=404/16=101/4
f'x=-4x-8y-13=0,即4x+8y=-13
f'y=-20y-8x-31=0,即4x+10y=-31/2
解得极值点:
x=-3/4
y=-5/4
f"xx=-4,f"yy=-20,f"xy=-8
4*20-8^2=80-64=16>0.因此有极值,且为极大值,其值
f(-3/4,-5/4)=1-2*9/16-10*25/16-8*15/16+13*3/4+31*5/4=(16-18-250-120+156+620)/16=404/16=101/4