Vrijeme: 21:05

Algebarske avanture prijatnog Lovre | Algebraic adventures of Lovre #3

Lovro se već lagano počelo vrtjeti od količine soka od šljive koji je popio, no ustrajno je odlučio riješiti još zadataka. Zgrabio je još jedan s police, a na njemu je pisalo:

Dan je niz od 5 pozitivnih realnih brojeva a_1,a_2, ... , a_5 t.d. za svaki prirodan i (1 \leq i \leq 5) vrijedi a_1+...+a_i \geq \sqrt{i}, odredi najveći M t.d. vrijedi

a_1^2 + ... +a_5^2 > M

Lovro was already slightly dizzy from the amount of plum juice he drank, but he persistently decided to solve more tasks. He grabbed another one off the shelf, and it went:

Given a sequence of 5 positive real numbers a_1,a_2, ... , a_5 so that for each natural number i (1 \leq i \leq 5) the expression a_1+...+a_i \geq \sqrt{i} is true, determine the largest M so that the following expression is valid:

a_1^2 + ... +a_5^2 > M