Question

Buna, este o serie de numere reale pe care nu stiu sa o dezvolt. Ma puteti ajuta?

Answer 1

 

$\displaystyle\\\frac{\sum_{i=1}^{10}ti}{10}=\frac{t\cdot1+t\cdot2+t\cdot3+t\cdot4+t\cdot5+t\cdot6+t\cdot7+t\cdot8+t\cdot9+t\cdot10}{10}=\\ \\=\frac{t(1+2+3+4+5+6+7+8+9+10)}{10}=\\\\\\=\frac{t\cdot\dfrac{10\cdot 11}{2}} {10}= \frac{t\cdot 5\cdot 11}{10}=\\\\\\=\frac{11t}{2}=\frac{11\cdot 21,\!44}{2}=11\cdot 10,72=\boxed{\bf 117,\!92}$