Question

The sum of AP:
5+12+19+26+...+145
is​

Answer 1

Step-by-step explanation:

here a=5

d=12-5=7

now 145=a+(n-1)d

145=5+(n-1)7

7n=140+7

n=21

so, Sn=n/2 *[a+l]

here l=last term=145

so, Sn= 21/2 * (5+145)

=21*75

=1575

hope it helps