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Find the sum of all the terms of an ap whose middle most terms is 30

Posted by Nageswararao Sakuru 6 years, 3 months ago

CBSE > Class 10 > Mathematics

1 answers

Sia ? 6 years, 3 months ago

Let a be the first term and d be the common difference of the given A.P.

Clearly, in an A.P. consisting of 11 terms, {tex} \left( \frac { 11 + 1 } { 2 } \right) ^ { t h }{/tex} i.e. 6^th term is the middle term.

{tex}\text{ it is given that the middle term =30}{/tex}

So a+5d=30 .....(1)

.{tex}S_{11}=\frac{11}{2}(2a+10d){/tex}

= 11(a+5d)

But a+5d=30 from (1)

Hence S₁₁= 11 × 30= 330

0Thank You

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