Question

Imi da exercitiul:
Intr-o progresie aritmetica a1=5 r=3
a)primii 5 termeni
b)a=15
c) S20

Answer 1

a1=5
a2=8
a3=11
a4=15
a5=18

a15=a1+14*r=5+14*3=5+42=47
s20=(a1+a20)*20:2=10(a1+a1+19*r)=10(10+19*3)=10(10+57)=670