Question

Se considera sirul : 1,2,11,16,21,...,4021 Intrebarile ...... A) Aflati cati termeni are sirul pana la 4021 ... B) Aflati termenul de pe locul 208. ....... C) Calculati suma S= 1+6+11+16+...+4021

Answer 1

A)

(4021-1):5+1=4020:5+1=804+1=805

B)

1=0×5+1
6=1×5+1
11=2×5+1
...

Formam regula:

Al n-lea termen=(n-1)×5+1
Al 208-lea termen=(208-1)×5+1=207×5+1=1036

C)

S=0×5+1+1×5+1+2×5+1+...+804×5+1
S=1×805 (termeni in total) + 5(0+1+...+804)
S=805+5×804×805:2
S=805+5×402×805
S=805+1618050
S=1618855