Question

Determinati termenul general si ratia unei progresii aritmetice in care Sn=3n^2+2n . Va roog ! Urgent !

Answer 1

$\it S_n =3n^2+2n$

$\it S_1 =a_1 = 3+2=5$

$\it S_2=a_1+a_2 =5+a_2= 3\cdot4+4=16 \Rightarrow a_2=16-5=11$

$\it r = a_2-a_1=11-5=6$

$\it a_n=a_1+(n-1)r = 5+(n-1)\cdot6=5+6n-6=6n-1$