Question

The sum of first 80 terms of an A. P whose 1st term is 6 and 80th term is 322 is _______​

Answer 1

$\huge\sf\pink{Answer}$

☞ Your Answer is 13120

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$\huge\sf\blue{Given}$

✭ First term = 6

✭ Last term (80) is 322

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$\huge\sf\gray{To \:Find}$

◈ The sum of the 80 terms?

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$\huge\sf\purple{Steps}$

We know that,

$\underline{\boxed{\sf S_n = \dfrac{n}{2}\bigg\lgroup a+l\bigg\rgroup}}$

◕ n = nth term = 80

◕ a = First term = 6

◕ l = Last term = 322

Substituting the given values,

➝ $\sf S_n = \dfrac{n}{2}\bigg\lgroup a+l\bigg\rgroup$

➝ $\sf S_{80} = \dfrac{80}{2} \bigg\lgroup 6+322 \bigg\rgroup$

➝ $\sf S_{80} = 40\bigg\lgroup 328 \bigg\rgroup$

➝ $\sf \orange{S_{80} = 13120}$

☯ $\sf \underline{\sf Know More}$

☆ $\sf a_n = a+(n-1)a$

☆ $\sf S_n = \dfrac{n}{2}[2a+(n-2)d]$

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