Question

(5+10+15......+75)+(3+6+9......+117)

Answer 1

Răspuns

Explicație pas cu pas:

(5*1+5*2+5*3+...+5*15)+(3*1+3*2+3*3+

+....+3*39)=

=5(1+2+3+...+15)+3(1+2+3+...+39)=

=5*15*16/2+3*39*40/2=

=5*15*8+3*39*20=

=600+2340=

=2940