Question

Calculati, utilizand propietatile adunarii:
a)3+6+9+12+..........+99;
b)5+10+15+............+2005

Answer 1

a)3*(1+2+3+4+...+33)=

=3*[33*(33+1)/2]=

=3*(33*34/2)=

=3*(1122/2)=

=3*561

=1683

b)5*(1+2+3+...+401)

=5*[401*(401+1)/2]

5*(401*402/2)

5*161202/2

5*80601

403005

(◠‿◕)(◠‿◕)(◠‿◕)