### Questions (332)

 33 How to find the sum of this series : $1+\frac{1}{2}+ \frac{1}{3}+\frac{1}{4}+\dots+\frac{1}{n}$ 17 Evaluate the limit $\lim\limits_{n \to \infty} \frac{1}{1+n^2} +\frac{2}{2+n^2}+ \ldots +\frac{n}{n+n^2}$ 14 Integrate : $\int \frac{x^2}{(x\cos x -\sin x)(x\sin x +\cos x)}dx$ 13 How to find the sum of this : $\sqrt{1+\frac{1}{1^2}+\frac{1}{2^2}}+ \sqrt{1+\frac{1}{2^2}+\frac{1}{3^2}}+\sqrt{1+\frac{1}{3^2}+\frac{1}{4^2}}+…$ 13 How to find the sum of the sequence $\frac{1}{1+1^2+1^4} +\frac{2}{1+2^2+2^4} +\frac{3}{1+3^2+3^4}+…$

### Reputation (4,366)

 +5 If $C_0,C_1,C_2,\cdots C_n$ denotes the binomial coefficients in the expansion of $(1+x)^n$ then $\sum^n_{r=0}\sum^n_{s=0} (C_r+C_s)$ =? -2 What is the proof that the total number of subsets of a set is $2^n$? +5 Given that $\;\sin^3x\sin3x = \sum^n_{m=0}C_m\cos mx\,,\; C_n \neq 0\;$ is an identity . Find the value of n. +5 Find the sum : $\sin^{-1}\frac{1}{\sqrt{2}}+\sin^{-1}\frac{\sqrt{2}-1}{\sqrt{6}}+\sin^{-1}\frac{\sqrt{3}-\sqrt{2}}{\sqrt{12}}+\cdots$

### Answers (22)

 3 Need help in proving that $\frac{\sin\theta - \cos\theta + 1}{\sin\theta + \cos\theta - 1} = \frac 1{\sec\theta - \tan\theta}$ 3 Solving $x^{\log(x)}=\frac{x^3}{100}$ 2 What is the proof that the total number of subsets of a set is $2^n$? 2 Finding minimum $\frac{x+y}{z}+\frac{x+z}{y}+\frac{y+z}{x}$ 2 How does one derive these solutions to the cubic equation?

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