Question

Calculați:
S=5/2+11/2+...+59/2
AJUTOR!

Answer 1

$S = \dfrac{5}{2}+ \dfrac{11}{2} +... + \dfrac{59}{2} \\ S = \sum\limits_{k=1}^{10}\dfrac{6k-1}{2} \\ S = \sum\limits_{k=1}^{10}\Big(3k-\dfrac{1}{2} \Big) \\ \\ S = 3\cdot \dfrac{10\cdot (10+1)}{2} - \dfrac{10}{2} \\ \\ S = 3\cdot 5\cdot 11 -5 \\ \\ S = 160$