1) Calculate and classify the critical points of the function (, ) = ^4 + ^4 2^2 + 4 2^2

2) Calculate the volume of the largest rectangular box that is in the first octant with three of its faces in the coordinate planes and one vertex in the plane x +2y +3z =6.

3) Use the Lagrange Multipliers method to obtain the extreme values of the function (, ) = subject to the constraint 9^2 + ^2 = 4.

i need the development about those three exercises.. Please, you explain step by step