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प्रश्न
The first and last terms of an AP are 17 and 350, respectively. If the common difference is 9, how many terms are there, and what is their sum?
उत्तर
Given that,
a = 17
l = 350
d = 9
Let there be n terms in the A.P.
l = a + (n − 1) d
350 = 17 + (n − 1)9
9n = 350 + 9 - 17
9n = 359 - 17
9n = 342
⇒ n = `342/9`
⇒ n = 38
Sn = `n/2(a+l)`
Sn = `38/2(17+350)`
= 19 × 367
= 6973
Thus, this A.P. contains 38 terms and the sum of the terms of this A.P. is 6973.
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