Sequences & Series Questions (847)

If the pth term of an A.P. is q and the qth term is p, then find its rth term.
Find the sum of \(n\) terms of the series \(\dfrac{4}{3} + \dfrac{10}{9} + \dfrac{28}{27} + \cdots\)
The sum of \(0.2 + 0.004 + 0.00006 + 0.0000008 + \cdots\) to ∞ is
If, for a positive integer \(n\), the quadratic equation, \(x(x+1) + (x+1)(x+2) + \cdots + (x+n-1)(x+n) = 10n\) has two consecutive integral solutions, then \(n\) is equal to
Divide 28 into four parts in an A.P. so that the ratio of the product of first and third with the product of second and fourth is 8:15. Find the four parts.
If \(x, y \in R^+\) such that \(x + y = 8\), then find the minimum value of \(\left(1 + \dfrac{1}{x}\right)\left(1 + \dfrac{1}{y}\right)\).
The value of \(3\displaystyle\sum_{n=1}^{\infty} \left(\frac{1}{\pi}\sum_{k=1}^{\infty} \cot^{-1}\left(1 + 2\sqrt{\sum_{r=1}^{k} r^3}\right)\right)^n\) is less than:
For Problems 7–9: In a G.P., the sum of the first and last terms is 66, the product of the second and the last but one is 128, and the sum of the terms is 126.If the decreasing G.P. is considered, then the sum of infinite terms is
For Problems 22–24: Two consecutive numbers from 1, 2, 3, …, \(n\) are removed. The arithmetic mean of the remaining numbers is \(\frac{105}{4}\).The removed numbers
In an A.P. of which \(a\) is the first term, if the sum of the first \(p\) terms is zero, then the sum of the next \(q\) terms is
Given series is: \(1^2 + 2 \cdot 2^2 + 3^2 + 2 \cdot 4^2 + 5^2 + 2 \cdot 6^2 + \cdots\). The sum of first \(n\) terms when \(n\) is even is \(\dfrac{n(n+1)^2}{2}\). Find \(S_n\) for odd \(n\).
If the equation \(x^3 + ax^2 + bx + 216 = 0\) has three real roots in G.P., then \(b/a\) has the value equal to ___.
The sum of series \(\dfrac{1}{2!} + \dfrac{1}{4!} + \dfrac{1}{6!} + \cdots\) is
\(\displaystyle\sum_{n=0}^{\infty} \dfrac{(\log_e x)^n}{n!}\) is equal to
Three positive numbers form an increasing G.P. If the middle term in this G.P. is doubled, the new numbers are in A.P. Then the common ratio of the G.P. is
A man saves ₹200 in each of the first three months of his service. In each of the subsequent months his saving increases by ₹40 more than the saving of immediately previous month. His total saving from the start of service will be ₹11040 after
For any three positive real numbers a, b and c, \(9(25a^2 + b^2) + 25(c^2 - 3ac) = 15b(3a + c)\). Then
If a, b, and c are in A.P., then \(a^3 + c^3 - 8b^3\) is equal to
Let \(a_1, a_2, a_3, \ldots, a_{10}\) be in G.P. with \(a_i > 0\) for \(i = 1, 2, \ldots, 10\) and \(S\) be the set of pairs \((r, k)\), \(r, k \in N\) (the set of natural numbers) for which \[\begin{vmatrix} \log_e a_1^r a_2^k & \log_e a_3^r a_4^k & \log_e a_5^r a_4^k \\ \log_e a_4^r a_5^k & \log_e a_6^r a_7^k & \log_e a_6^r a_8^k \\ \log_e a_7^r a_8^k & \log_e a_9^r a_9^k & \log_e a_9^r a_{10}^k \end{vmatrix} = 0\] Then the number of elements in \(S\) is:
The value of \(2^{1/4} \cdot 4^{1/8} \cdot 8^{1/16} \cdots \infty\) is
Which term of the sequence \( 25, 22\dfrac{3}{4}, 20\dfrac{1}{2}, 18\dfrac{1}{4}, \ldots \) is numerically smallest?
The sum of all two digit positive numbers which when divided by 7 yield 2 or 5 as remainder is __________.
The fifth term of a G.P. is 2. Find the product of the first 9 terms of the G.P.
The greatest integer by which \(1 + \sum_{r=1}^{30} r \times r!\) is divisible is
Let p be the first of n arithmetic means between two positive numbers and q be first of n harmonic means between same two numbers. Then \(\frac{p}{q}\) can lie in interval(s)
Let A1, G1, H1 denote the arithmetic, geometric and harmonic means, respectively, of two distinct positive numbers. For n ≥ 2, let An–1 and Hn–1 have arithmetic, geometric and harmonic means as An, Gn, Hn respectively. Which one of the following statements is correct?
If l, m, n are three numbers in G.P., then the ratio of first term to the common difference of an A.P. whose lth, mth and nth terms are in H.P. is equal to
In a geometric progression consisting of positive terms, each term equals the sum of the next two terms. Then the common ratio of this progression equals
Let $S_a$ denote the sum of first $n$ terms of an arithmetic progression. If $S_{20}=790$ and $S_{10}=145$, then $S_{15}-S_5$ is:
If \(x = \displaystyle\sum_{n=0}^{\infty} a^n\), \(y = \displaystyle\sum_{n=0}^{\infty} b^n\), \(z = \displaystyle\sum_{n=0}^{\infty} c^n\) where a, b, c are in AP and \(|a| < 1\), \(|b| < 1\), \(|c| < 1\), then x, y, z are in
If the sides of a right angled triangle form an AP, the sines of the acute angles are
The sum of all values of \(\theta\) in interval \([0, 4\pi]\) for which \(\sin\theta, \cos\theta, \tan\theta\) taken in that order constitute a geometric progression is
The sum of the series \(\frac{1}{1 + 1 + 1^2} + \frac{2}{1 + 2 + 2^2} + \frac{3}{1 + 3 + 3^2} + \cdots\) to n terms is
If three successive terms of a G.P. having common ratio r form the sides of a triangle, then the possible value(s) of \([r]\) is/are (where \([\cdot]\) denotes greatest integer function)
If \(a_1, a_2, a_3, \ldots\) are in arithmetic progression, then \(S = a_1^2 - a_2^2 + a_3^2 - a_4^2 + \ldots - a_{2k}^2\) is equal to:
If \(a, b, c\) are in AP and \((a + 2b - c)(2b - c + a)(c + a - b) = 9abc\), then the common difference is
Let \(a + ar_1 + ar_1^2 + \cdots + \infty\) and \(a + ar_2 + ar_2^2 + \cdots + \infty\) be two infinite series of positive numbers with the same first term. The sum of the first series is \(r_1\) and the sum of the second series is \(r_2\). Then the value of \((r_1 + r_2)\) is ___.
Let \(a_1, a_2, a_3, \ldots\) be terms of an A.P. If \(\frac{a_1 + a_2 + \ldots + a_p}{a_1 + a_2 + \ldots + a_q} = \frac{p^2}{q^2}\), \(p \neq q\), then \(\frac{a_p}{a_q}\) equals
The numbers 1, 4, 16 can be three terms (not necessarily consecutive) of
Let A1, G1, H1 denote the arithmetic, geometric and harmonic means, respectively, of two distinct positive numbers. For n ≥ 2, let An–1 and Hn–1 have arithmetic, geometric and harmonic means as An, Gn, Hn respectively. Which one of the following statements is correct?
Let A1, G1, H1 denote the arithmetic, geometric and harmonic means, respectively, of two distinct positive numbers. For n ≥ 2, let An–1 and Hn–1 have arithmetic, geometric and harmonic means as An, Gn, Hn respectively. Which one of the following statements is correct?
The value of \(\displaystyle\sum_{i=1}^{n} \sum_{j=1}^{i} \sum_{k=1}^{j} 1 = 220\), then the value of \(n\) equals
If a,b,c are in AP, then (a - c)? equals
Let there be a G.P. whose first term is 'a' and common ratio is 'r'. If A and H are the arithmetic mean and the harmonic mean respectively for the first 'n' terms of the G.P. Then \(A \times H\) is equal to
the sum of the first seven terms to the sum of the first eleven terms is 6 : 11 and the seventh term lies in between 130 and 140, then the common difference of this A.P. is [JEE (Advanced) 2015] be
The value of expression $[\sqrt{1}] + [\sqrt{2}] + [\sqrt{3}] + ... + [\sqrt{100}]$ (where $[.]$ denotes greatest integer function) is equal to ____.
Let Sn, S2n, S3n are respectively the sums of first n, 2n, 3n terms of an arithmetic progression, then S3n =
Let \(x, y\) are real numbers such that \(x, x + 2y, 2x + y\) form an A.P. while the numbers \((y + 1)^2, xy + 5, (x + 1)^2\) form a G.P., then \(|x| - |y|\) is equal to
Find the sum: \(1^3 - 2^3 + 3^3 - 4^3 + \ldots + 9^3\)
Let \(T_r\) be the \(r\)th term of an A.P. whose first term is \(a\) and common difference is \(d\). If for some positive integers \(m, n\) with \(m \neq n\), \(T_m = \frac{1}{n}\) and \(T_n = \frac{1}{m}\), then \(a - d\) equals