Răspuns:
Explicație pas cu pas:
a) 1+3+5+...+11=1+3+5+7+9+11=36=6²
b) 1+3+5+...+19=1+3+5+7+9+11+13+15+17+19=100=10²
c)
S=1+3+5+...+2k-1
S=2k-1+2k-3+...+1
---------------------------
2S=2k+2k+...+2k
Aflam cati termeni sunt:
(2k-1-1):2+1=(2k-2):2+1=k-1+1=k
=>2S=2k*k => S=k*k => S=k²
