- #1
sandy.bridge
- 798
- 1
Homework Statement
Find extreme values for
[tex]f(x, y, z)=x+y+z[/tex]
subject to:
[tex]x^4+y^4+z^4=c>0[/tex]
Therefore, since c>0, exclude the origin.
Let [tex]L(x, y, z, \lambda{)}=x+y+z+\lambda{(}x^4+y^4+z^4-c)[/tex]
and thus
[tex]L_1(x, y, z, \lambda{)}=1+4x^3\lambda[/tex]
[tex]L_2(x, y, z, \lambda{)}=1+4y^3\lambda[/tex]
[tex]L_3(x, y, z, \lambda{)}=1+4z^3\lambda[/tex]
[tex]L_4(x, y, z, \lambda{)}=x^4+y^4+z^4-c[/tex]
with solutions
[tex]x=y=z=(-1/4\lambda{)}^{1/3}[/tex]
and
[tex]0=((-1/4\lambda{)}^{1/3})^4+((-1/4\lambda{)}^{1/3})^4+((-1/4\lambda{)}^{1/3})^4-c=3((-1/4\lambda{)}^{1/3})^4-c[/tex]
[tex]c=-1/(4c^{3/4})[/tex]
and since c>0, the question has no solutions.