Question

If the nth term of an arithmetic progression is given by -7- 6n, then what is the
sum of the first 20 terms of the AP?

Answer 1

Answer:

since -7-6n is nth term

a1=-7-6×1

=-13

a2=-7-6×2

=-19

d=a2-a1

=-19-(-13)

=-6

S20=n/2 (2a+(n-1)d)

=10(2×-13+19×-6)

=-1400