Chercher les extrémums des fonctions \(f(x,y)\) suivantes :
1
\(3xy - x^3 - y^3\)
2
\(-2(x-y)^2+x^4+y^4\)
3
\(x^2y^2(1+3x+2y)\)
4
\(2x+y-x^4-y^4\)
5
\(\frac {xy}{(x+y)(1+x)(1+y)},\ x,y> 0\)
6
\(xe^y + ye^x\)
7
\(x(\ln^2x + y^2)\), \(x>0\)
8
\(\sqrt{x^2+(1-y)^2} + \sqrt{y^2+(1-x)^2}\)
9
\(MA+MB-MO\),\(O = \text{mil}(A,B)\)