Question

How many terms of the A.R 18, 16, 14, . be taken so that their sum is zero?

Answer 1

See the attachment here


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Answer 2

Answer:

19

Step-by-step explanation:

Number series = 18, 16, 14

First term = a1 = 18

Common Difference = d = a2 - a1 = 16 - 18 = -2

Find the nth term:

an = a1 + (n - 1)d

an = 18 + (n - 1)(-2)

an = 18 -2n + 2

an = 20 - 2n

Find the number of terms:

The sum is zero

n/2 (a1 + an) = 0

n/2( 18 + 20 - 2n) = 0

n/2(38 - 2n) = 0

n(19 - n) = 0

n = 0 or 19 - n = 0 (reject n = 0)

n = 19

Answer: 19 terms