Question

calculati suma 1+3+5+...+21 dau coroana

Answer 1

Ti-o rezolv cu formula lui Gaus.
S=1+2+3+4+5+...+20+21-(2-4-...-20)
S=$\frac{21*22}{2}$-2*$\frac{10*11}{2}$
S=21*11-5*11
S=16*11
S=176

Sper ca nu am gresit la calcule, macar sper ca ai inteles ideea :D

Answer 2

$\boxed{ 1+3+5+...+a = \Big(\dfrac{a+1}{2}\Big)^\big2} \rightarrow formula \\ \\ \\ 1+3+5+...+21 = \Big(\dfrac{21+1}{2}\Big)^\big2 = \Big(\dfrac{22}{2}\Big)^\big2 = 11^2 = 121$