Question

Cunoscand suma Sn a primilor n termeni ai unei progresii aritmetice , gasiti primul termen si ratia progresiei daca:
Sn= n²-2n , oricare ar fi n≥1

Sn=2n²-n, oricare ar fi n≥1

Answer 1

[tex]a)a_1=S_1=1-2=-1\\ a_2=S_2-S_1=0-(-1)=1\\ r=a_2-a_1=1-(-1)=2\\ \\ b)a_1=S_1=1\\ a_2=S_2-S_1=6-1=5\\ r=a_2-a_1=5-1=4[/tex]