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The second and the last term of an A.P. are 18 and 720 respect

Question

The second and the last term of an A.P. are $18$ and $720$ respectively and their common difference is $6$ . What is their sum?

S_{n} = 48, 665

S_{n} = 43, 554

S_{n} = 43, 665

S_{n} = 42, 665

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Daniel Discussed

The second and the last term of an A.P. are

18

and

720

respectively and their common difference is

6

. What is their sum?

9 mins ago

Discuss this question LIVE

9 mins ago

Text solutionVerified

Given that,

a_{2} = 18

; last term,

l = 720, d = 6

d = a_{2} - a_{1}

6 = 18 - a_{1}

a_{1} = 12

We know that, last term,

l = a + (n - 1) d

\Rightarrow 720 = 12 + (n - 1) 6

\Rightarrow 720 = 12 + 6 n - 6

\Rightarrow 720 - 6 = 6 n

\Rightarrow n = \frac{714}{6}

\Rightarrow n = 119

We know

S_{n} = \frac{n}{2}

[First term

+

Last term]

= \frac{119}{2} [12 + 720]

= 59.5 [732]

Therefore,

S_{n} = 43, 554

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Question Text	The second and the last term of an A.P. are $18$ and $720$ respectively and their common difference is $6$ . What is their sum?
Answer Type	Text solution:1
Upvotes	150