Question

F an = 9 – 5n show that a1 ,a2 ,…….Are in ap .Also find sum of first 15 terms of ap.

Answer 1

a1=9-5(1)=4
a2=9-5(2)=-1
a3=9-5(3)=-6
d=-5
s15 =n/2(2a+(n-1) d)
=15/2(2(4)+14(-5)
=15/2(8-70)
=15/2(-62)
=15×-31
=-465
hope this is correct and helps