Question

Find the middle term of the AP 7,11,15.......139. Also find the sum of all the terms of the AP

Answer 1

AP = A+(N-1)D

139 = 7+(N-1) 4

139-7 = (N-1) 4

132/4 = N-1

33 = N-1

34 = N

SUM OF AP = N/2 (A+AN)

SUM OF AP = 34/2 (7+139)

==> 17(146)

==> 2482

ANS = 2482

I HOPE ITS HELPFUL

Answer 2

Hi friend..............
a= first term = 7
d= 11- 7=4
an=a+(n-1)d
an=139
139=7+(n-1)4
139-7=(n-1)4
132=4n-4
132+4=4n
136=4n
n=136/4
n=34.
to find middle term of an even AP,there are two formulas, and they are:-
n/2 and (n/2+2)
1) n/2 =34/2
=17
2) (n/2+2) = 34/2+2
=34+4/2
=38/2
=19.
So two middle terms of this A.P. are 17 and 19.
#Hope it helps#