Question

find the sum of the first 15 terms of an AP whose nth term is 9-5n

Answer 1

Let n=1
9-5×1=4

Now,n=15
9-5×15= -66

Sn = n/2(a+l)
=15/2(4-66)
= 15×-31
=-465

Answer 2

Answer:

hope it's help you......