Question

If Sn=3n2+5n. Find the cd

Answer 1

sn=3n×2+5n
s1=3(1)2+5(1)
s1=3×2+5
=6+5
s1=a1=11
s2=3(2)×2+5×2
=6×2+5×2
=12+10
s2=22
s2=a1+a2
22=11+a2
22-11=a2
a2=11
cd=a2-a1
=11-11
cd=0