Question

if the first n terms of the arithmetric sequence 20, 18, 16, are added how many of these terms will be added to get a sum of -100?

Answer 1

Answer:

25

Step-by-step explanation:

here a=20

d=-2

S=-100

we know that S =n/2(2a+(n-1)d)

by substituting a,d,S

we get the eqn,       n^2-21n-100=0

                                 (n-25)(n-4)=0

n=25 is the ans  (note here n=-4 is not possible)

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