Question

If sn =3n+1 sn-1= 2n-1,then find the an

Answer 1

Answer:

sn=3n+1

s1=3×1+1=4=a1

s2=3×2+1=7=a1+a2

S2-S1=a2=7-4=3

d=a2-a1=3-4=-1

an=a1+(n-1)d

=4+(n-1)(-1)

=4-n+1

=5-n