find all the relative maxima, minima and saddle points of each of the following

a) f(x,y)=3x^2+6xy+7y^2-2x+4y

b) f(x,y)=x^3 - y^3 - 2xy+6

c) f(x,y)=4xy-x^4-y^4

problem 2) determine the dimensions of rectangular box, open at the top, having a volume of 32 cubic ft. Requiring the least amount of material for its construction.

thanks for your help....these work out problem to practice for the exams. need your help...thanks