If the 10th term of an AP is 47 and its first term is 2,find the sum of its first 15 terms.
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If the 10th term of an AP is 47 and its first term is 2,find the sum of its first 15 terms.
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Answer:
Sum of first 15 terms in given A.P = 555
Step-by-step explanation:
Let a , d are first term and common difference of an A.P
a = 2 (given )
/* we know that,
*/
i ) Now ,
$\implies d = \frac{45}{9}$
$\implies d = 5$ ---(1)
ii ) Sum of first n terms in A.P
(Sn) =
Here, substitute n = 15, a = 2, d = 5, we get
=
= $\frac{15}{2}\times 74$
= $ 15 \times 37$
= $ 555 $
Therefore,
Sum of first 15 terms in given A.P = 555
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