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**dopi** Basically i'v been given the following function

Let f(x, y, z) = ln ( (x^7)*(y^11)*(z^2)) − 2xy − 11y − 7z, where x > 0, y > 0, z > 0.

and i want to find the values of x, y and z at any critical point(s) of this function, and hence determine any local maximum or minimum values of f(x, y, z).

So far i have have found partial df/dx =0. df/dy=0 and df/dz=0

From that i found that:

**x= 77/8**

y=8/11

z=2/7

The thing is with a f(x,y) problem i can determine da local max and min and saddle point but im a bit stuck with this one as it as a 3rd variable z. so icant seem to determine it for a f(x,y,z) problem

any help? Thankz