1+3+5+...+117=
1+2+3+4+5+6+...+176+176-(2+4+6+...+176)
aplicam formula lui Gaus care era:
1+2+3+...n=n (n+1)supra 2
[tex] \frac{177(177 + 1)}{2} - \frac{176(176 + 1)}{2} = [/tex]
[tex] \frac{177 \times178 }{2} - \frac{176 \times 177}{2} = [/tex]
[tex]177 \times 89 -88 \times 177 = [/tex]
dam factor comun pe 177
[tex]177(89 - 88) \\ 177 \times 1 = 177[/tex]
