find all critical points of the function fxy 2yx423y332x ind
find all critical points of the function f(x,y) =2yx^4+(2/3y)^3-32x. indicate whether each such point gives a local maximum, a local minimum , or whether it is a saddle point.
Solution
f(x,y)=2yx^4+(2/3y)^3-32x.
fx(x,y)=8*y*x^3-32
fxx(x,y)=24*y*x^2
fy(x,y)=2*x^4-(8/9)*(1/(y^4))
fxy(x,y)=8*x^3
now critical point:-
fx(x,y)2*x^4-(8/9)*(1/(y^4))=0 ==>x^4 * y^4=0
and
fy(x,y)=2*x^4+2*y^2=0 ==>x^4+y^2=0
only possible if (x,y)=(0,0)
at (0,0)
fxx(x,y)=24*y*x^2=0
fxy(x,y)=8*x^3=0
so D=fxx*fyy-fxy^2=0
hence no conclusion can be done
