What i did is i set

, what's true for

. This itself is a linear function with a negative slope, but the function is always positive before

. It starts from B and does down linearly untill

. So theoretically the overall function increases untill

, after this point, the partial derivative gets negative (

for

) and henceforth starts from then on decreasing the overall function.

Is it correct that i thus say, the maximum of the function with three varibales is the same as the one with two, except for

?

Thank you

Schdero