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Suma de patrate e patru
Posted:
Wed Jun 03, 2009 7:33 pm
by
alex2008
Fie
\( a,b,c,d \)
trei numere reale satisfacand constrangerea
\( a^2+b^2+c^2+d^2=4. \)
Sa se demonstreze ca
\( a^3+b^3+c^3+d^3\le 8. \)
Posted:
Wed Jun 03, 2009 9:44 pm
by
Marius Mainea
\( \sum a^3\le 2\sum a^2=8 \)