... [ 1-( X/3 +Y/3)+ (X/3 +Y/3)2 -( X/3 +Y/3)3 + o(ρ3)]= + X - Y - X2 + Y2 + XY + X3 - Y3 - XY2 + o(ρ3)= + (x-2) - (y-1) - (x-2)2 + (y-1)2 + (x-2)(y-1) + (x-2)3 - (y-1)3 - ... 2(0,0)d ff’x= 2sin(x-y)cos(x-y)=sin2(x-y)f’’xx= 2cos2(x-y)=> f’’xx(0,0)=2f’’xy= -2 cos(x-y)=> f’’xy(0,0) =-2 f’y= 8y-2sin(x-y)cos(x-y)=8y-sin2(x-y)f’’yy= 8+2cos2(x-y) => f’’yy(0,0)=10 ... x=1,y=0 v x =-1 ,y=0Xét: L(x,y,λ)= +λ(x2+y2 -4 ) x=0,y= , λ =-5 e5 v x= ,y=0, λ =-3 e -3 f(0,0)=0 f(1,0) =-1 f (-1 ,0)=1f(0,2)= f(0 ,-2 )=4e5f(2,0)= f (-2 ,0) =-4 e -3 Maxf=4e5x2+y24Minf =-1 x2+y24Câu...