a) Bfli toan QHIT t6ng quat: min f(x) , n€u co X i= 0 va f(x) bi cMn du6"i tren t~p phuong an x
t XEX
thi se luon luon co phuong an Cl,l'C bien t6i uu (phuong an cO' ban t6i un).
b) 0 bang don hinh tOi un, n€u Llv = ° v6"i Xv Ia bi€n tl,r do (hi€n phi cO'[r]