Question

3+6+9+.........................+78+81

Answer 1

suma=3+6+9+...+78+81
suma=81+78+...+9+6+3
-----------------–-----------
suma•2=84+84+84+..+84+84
....}de 81 ori ( pt ca este cel mai mare numar )
84•81=6.804(2•suma)
6.804:2=3.402(suma)


Sper ca te-am putut ajuta :)))