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Question
If `sum_("r" - 1)^"n" (2"r" + 1) = 440,` then n = _____.
Options
20
22
21
19
MCQ
Fill in the Blanks
Solution
If `sum_("r" - 1)^"n" (2"r" + 1) = 440,` then n = 20.
Explanation:
We have, `sum_("r" - 1)^"n" (2"r" + 1) = 440`
⇒ 3 + 5 + 7... + (2n + 1) = 440
⇒ `"n"/2[2 xx 3 + ("n" - 1)(2)] = 440`
⇒ n(3 + n - 1) = 440
⇒ n(n + 2) = 440
⇒ n = 20
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Definite Integral as Limit of Sum
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