## $n$th derivative of $\frac 1{f(x)}$

Is there a closed-form solution for $\frac {d^n}{dx^n}\frac 1{f(x)}$? I’ve looked at the first five derivatives in search of some pattern, but I can’t identify anything strong enough to give a closed formula. Answer It’s not exactly a closed form, but Faà di Bruno’s formula \frac{d^n}{dx^n} f(g(x))= \sum_{k_1 + 2k_2 + \ldots + n k_n … Read more

## n2(n2−1)(n2−4)n^2(n^2-1)(n^2-4) is always divisible by 360 (n>2,n∈N)(n>2,n\in \mathbb{N})

How does one prove that n2(n2−1)(n2−4) is always divisible by 360? (n>2,n∈N) I explain my own way: You can factorize it and get n2(n−1)(n+1)(n−2)(n+2). Then change the condition (n>2,n∈N) into (n>0,n∈N) that is actually equal to (n∈N). Now the statement changes into : n(n+1)(n+2)2(n+3)(n+4) Then I factorized 360 and got 32⋅23⋅5. I don’t know how … Read more

## Erroneously Finding the Lagrange Error Bound

Consider $f(x) = \sin(5x + \pi/4)$ and let $P(x)$ be the third-degree Taylor polynomial for $f$ about $0$. I am asked to find the Lagrange error bound to show that $|(f(1/10) – P(1/10))| < 1/100$. Because $P(x)$ is a third-degree polynomial, I know the difference is in the fourth degree term. So I found the … Read more

## General solution of the equation sin2015(x)+cos2015(x)=1∀x∈R\sin^{2015}(x)+\cos^{2015}(x) = 1\; \forall \; x\in \mathbb{R}

Calculation of General solution of the equation sin2015(x)+cos2015(x)=1∀x∈R. MyTry: We can Write the equation as sin2015(x)+cos2015(x)≤sin2(x)+cos2(x)=1. And equality hold when sin(x)=1 and cos(x)=0. So we get x=nπ+(−1)n⋅π2 and x=2nπ±π2. Now How can I calculate common solution of sin(x)=0 and cos(x)=0. Please help me. Thanks. Answer Your approach seems correct although sin(x)=cos(x)=0 is just nonsense. You … Read more

## Alternative to Rolle’s Theorem?

I sincerely hope this is not a dumb question. I was doing some reading through an analysis book and was looking at Rolle’s Theorem. That is, if a function f:[a,b]:→R is continuous on [a,b] and differentiable on (a,b), and that f(a)=f(b). Then ∃c∈(a,b) such that f′(c)=0. Now, it seems to me that the intuition here … Read more

## Is this function a continuous function?

If I define a function over the non rational numbers: f:R∖Q→R f(x)=1 is it continuous ? I think it is because all the points on the domain in any interval have f(x)−1=0 Answer Yes, this function is continuous. Let’s prove it rigorously. Let ϵ>0. Let x∈R−Q. We want to find some δ>0 such that |x−y|<δ … Read more

## How many times between 22 pm and 44 pm does the minute hand coincides with second hand.?

How many times between 2 pm and 4 pm does the minute hand coincides with second hand.? options a.)\quad 118 \\ b.)\quad 119\\ c.)\quad 120\\ d.)\quad 121\\ Number of rounds of full circle by second’s hand in 2 hours =120. Number of rounds of full circle by minutes’s hand in 2 hours =2. so is … Read more

## Prove cc satisfies the integral

If f:[0,1]→R is continuous, show that there exists c∈[0,1] such that f(c)=∫102tf(t)dt. So it’s pretty clear to me that I have to use Intermediate Value Theorem and Cauchy-Schwarz inequality but I can’t quite get the trick done. Any help appreciated. Answer Since f is continuous there exist a,b∈[0,1] such that f(a)≤f(x)≤f(b),∀x∈[0,1]. Now, t∈[0,1]⟹tf(a)≤tf(x)≤tf(b). So 2f(a)∫10tdt≤2∫10tf(t)dt≤2f(b)∫10tdt. … Read more

## Subtraction of a number

I have a number $x$. If I remove the last digit, I get $y$. Given $x-y$, how can I find $x$? For example x=34 then y=3 given 34-3=31, I have to find 34. if x=4298 then y=429 , given 4298-429 = 3869 . how can I find 4298 from given 3869? Answer Removing the last … Read more

## Wonder how to evaluate this factorial (−12)!\left(-\frac{1}{2}\right)!

I’ve learned factorial. But today I saw a question which I don’t know how to start with: (−12)! Can anyone explain how to solve it? Thanks Answer As suggested by Workaholic, I=(−12)!=Γ(12)=∫+∞0x−1/2e−xdx=2∫+∞0e−y2dy=∫Re−y2dy and by Fubini’s theorem: I2=∫R2e−(y2+z2)dydz=∫2π0∫+∞0ρe−ρ2dρdθ=π∫+∞02ρe−ρ2dρ=π so: (−12)!=√π. AttributionSource : Link , Question Author : Mathxx , Answer Author : Jack D’Aurizio