Question

if an=5-2n, find AP and also find S20

Answer 1

if an=5-2n
a1=5-2=3
a2=5-4=1
a3=5-6=-1
A.P.→3,1,-1,-3,-5....
here d=-2
and a=3
s20=20/2(2×3+19×-2)
s20=10(6-38)
s20=-320