a-5) Write the equation used to find the locations of the extrema of f(x,y)= xy + 2xy³

on a circular disk given by x² + y² ≤9 using the method of substitution. Do not solve for the

extrema.

b-) A cylindrical metal can is to be manufactured from a fixed amount of sheet metal.

Use the method of Lagrange multipliers to determine the ratio between the dimensions of the can with the largest capacity.