Question

Find the sum of the first 19 terms of the ap whose nth term is given by an=7-4n

Answer 1

Answer:

Step-by-step explanation:

an=7-4n

Put n=1

a1=7-4*1=3

Put n=2

a2=7-4*2=-1

d=-4

Sn=19/2[2*3+(19-1)-4]

=19/2(6-75)

=19/2*-66

=-627