Mathematics I20775 marksNumerical: Local extrema saddle pointsMaximum and minimum values
Find the local maximum and minimum values, saddle points of f(x,y) = x4 + y4 - 4xy + 1.
Find the local maximum and minimum values, saddle points of $f(x,y) = x^4 + y^4 - 4xy + 1$. [5]
Function: $f(x,y) = x^4 + y^4 - 4xy + 1$ $$ fx = 4x^3 - 4y = 0 ;\Rightarrow; y = x^3 \tag{1} $$ $$ fy = 4y^3 - 4x = 0 ;\Rightarrow; x = y^3 \tag{2} $$ Substitute (1) into (2): $$x = (x^3)^3 = x^9 ;\Rightarrow; x^9 - x = 0 ;\Rightarrow; x(x^8 - 1) = 0$$ So $x = 0$ or