Question

How many terms of the sequence 8, -6, - 4, ... must be
taken, so that their sum is 70.
How many terms of the sequence 18, 16, 14, ... should be taken
so that their sum is zero.
(M.D.U. Jan. 2010)
100​

Answer 1

Step-by-step explanation:

sequence = 18,16,14...

a=18 d=(-2)

Sn=0

Using Formula

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

Putting values

0=n/2(2(18)+(n-1)(-2))

0=n(36-2n+2)

0=(-n)+38

-38=-n

n=38