Question

In the given AP 1, 4, 7, ........... How many teem make a sum 51.
step by step ​

Answer 1

Answer:

6 terms would be required

Step-by-step explanation:

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Answer 2

Answer:

No. of terms required, n = 6.

Step-by-step explanation:

a = 1

d = 3

Sₙ = 51 = n [2a+(n-1)d] / 2

⇒ 51 = n [2 + 3n - 3]/2

⇒ 102 = n (3n - 1)

⇒ 3n² - n - 102 = 0

⇒ 3n² - 18n + 17n - 102 = 0

⇒ 3n (n-6) + 17(n-6) = 0

⇒ (3n+17)(n-6) = 0

⇒ n = 6, (-17/3)                  

[(-17/3) is not possible since, the no. of terms is always a natural no.]

So, n = 6.

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