Questions on the evaluation of derivatives or problems involving derivatives (for example, use of the mean value theorem).

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1answer
29 views

Is this function increasing? (standard normal distribution, Mills Ratio)

Where $\phi\left(z\right)$ and $\Phi\left(z\right)$ represent the standard normal pdf and cdf respectively. 1) Is the function $f\left(z\right)=\dfrac{\phi\left(z\right)}{1-\Phi\left(z\right)}$ ...
1
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3answers
19 views

Indefinite integrals with rati0nal and polynomial functions and Substituion

I am totally confused with the substitution method of evaluating indefinite integrals, especially those with rational functions and polynomials. I have 2 cases, which if I made to understand, would ...
0
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1answer
14 views

Rate of change question involving velocity, displacement and acceleration

I have been having trouble understanding questions c)-e) and am in need of some help: An object is moving in a straight line from a fixed point. The displacement $s$ in metres is given by ...
0
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0answers
28 views

What is the derivative of this?

I have a function of the following form: $J = \|W^TW-I\|_F^2$ Where, $W$ is a matrix and $F$ is the Frobenius Norm. How can I find the derivative of $\frac{\partial J}{\partial W}$ ?
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0answers
20 views

Derivatives in Topological Vector Spaces and General Spaces

I know that we may have a function $f$ such that all the directional derivative of $f$ in some topological vector space $V$, but the derivative need not exist. Moreover, it's possible for all the ...
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0answers
13 views

Partial integration and substition rule.

Well in my day to day usage I now came upon an example of using the substition rule where I can't see how it works, and I wonder how one could handle such an equation with ease. The set of equations ...
3
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1answer
17 views

Problem with the type of equation $\sqrt{x}+\sqrt{y} = \sqrt{a}$ and vertices?

I am asked to find the type equation $\sqrt{x}+\sqrt{y} = \sqrt{a}$ , represents ? i.e a parabola , or hyperbola or ellipse or circle by squaring twice? Now , what I have done is like this ...
2
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1answer
44 views

Can this special case happen when working with L'Hopitals rule?

I am using this version of L'Hopital's rule Assume that $\lim_{x \rightarrow a}f(x)=\lim_{x \rightarrow a}g(x)=0$, and that the limit-value $\lim_{x \rightarrow a} \frac{f'(x)}{g'(x)}$ exists (could ...
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1answer
32 views

Can we claim that $f(x)$ is an increasing function and its stationary point is $x = \infty$ (in this specific case)?

If $f(x)$ is concave and its first derivative $f'(x) \rightarrow 0$ when $x\rightarrow \infty$, can we claim that $f(x)$ is an increasing function and its (only) stationary point is $x = \infty$ ? ( ...
0
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2answers
28 views

is it possible to intergrate this function to get x(t) and y(t)?

say you have a function as below; $d^2V(t)/dt = -B^2V(t)$ B is a constant Initial conditions $V_x(0) = V$, $V_y(0) = 0$ I can't see how to integrate to get x(t) and y(t); I ended up with ...
3
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2answers
285 views

Calculating derivative using definiton for $f(x)=\frac{x - \sin x}{x^2}$

Really stuck on this one.... $\displaystyle f(x) = \frac{x - \sin{x}}{x^{2}}$ for $x \neq 0$ and $0$ when $x = 0$ Using the definition of the derivative, find $f'(0)$ I know the definition is ...
1
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1answer
1k views

Using the limit definition to find a derivative for $2\sqrt{x-3}$

I am trying to find the derivative of $2\sqrt{x-3}$ using the limit definition of a derivative. What I did is $$\lim_{h \to 0} \frac {2 \sqrt {(x+h)-3} -2 \sqrt {x-3)})}{h}$$ I multiplied the ...
2
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2answers
1k views

Definition of derivative $f(x) = \sqrt{3-5x}$

I am not sure how to factor this out $$f(x) = \sqrt{3-5x}$$ I then make it $f(x) = \frac {\sqrt{3-5(x+h)} - \sqrt{3-5x}}{h}$ I tried to multiply by the first time + the second term from the ...
6
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3answers
4k views

Finding derivative of $\sqrt{9-x}$

I am trying to find the derivative of $\sqrt{9-x}$ using the definition of a derivative $$\lim_{h\to 0} \frac {f(a+h)-f(a)}{h} $$ $$\lim_{h\to 0} \frac {\sqrt{9-(a+h)}-\sqrt{9-a}}{h} $$ So to ...
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1answer
23 views

is split function derivable

$ f(x) = \begin{cases} \frac{sin(x)}{x}, & x \ne0 \\ x+1, & x=0 \end{cases}$ I know that the function is a continuous function in R. But is this function derivable at x=0? I am not sure.. ...
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1answer
13 views

Estimating values using tangent line? [on hold]

How do you do this type of question and what would be correct answers in this case? Thank you all in advance!
4
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1answer
314 views

Derivation of Euler-Lagrange equation

Here is a simple (probably trivial) step in the derivation of the Euler-Lagrange equation. If we denote $Y(x) = y(x) + \epsilon \eta(x) $, I want to know why is $\dfrac{\partial ...
2
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1answer
36 views

Integral inequality $\int_0^x{f(t)^3 dt \leq \left( \int_0^x f(t) dt\right)^2} :\forall x>0$

Let $f(0) = 0$ and $0<f'(x)\leq1$ for all $x \geq0$, then prove: $$\int_0^x{f(t)^3 dt \leq \left( \int_0^x f(t) dt\right)^2} :\forall x>0$$ The hint I was given was "differentiate, factor and ...
6
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1answer
1k views

Meaning of different Orders of Derivative

I have been trying to analyse the meaning of higher order derivatives and their geometrical significance. Given a function $f(x)$ what are the unique geometric interpretation of its higher orders? ...
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0answers
16 views

Numerical integration of function with derivatives of implicit variables

I have an independent (array) variable $r = {r_0, r_1, ..., r_N}$, and three functions (arrays) of that variables, $n(r) ={n_0, n_1, ..., n_N}$, $p(r)$, and $E(r)$. How can I calculate the function ...
4
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4answers
190 views

Chain rule for partial derivatives intuition

Can somebody give me an intuitive explanation for the above equations. I'm not sure how they come about and how they can be perceived logically. $$\frac{\partial z}{\partial s} =\frac{\partial ...
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3answers
765 views

Any ideas on how I can prove this expression?

I don't have a lot of places to turn because i am still in high school. So please bear with me as i had to create some notation. In order to understand my notation you must observe this identity for ...
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0answers
58 views
+50

Analyze the variation of this function $f(x)=x \exp[a+b(x-1)] \, E_1[a+b (x-1)]$ w.r.t. $x$

Please, I need to analyse the variation of the following function w.r.t. $x$ : $f(x)=x \exp[a+b(x-1)] \, E_1[a+b (x-1)]$, where $E_1[a+b (x-1)]$ is the exponential integral, $b>a$, $a>0$, ...
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1answer
33 views

$ \exists c \in( a, b) \text{ such that } f(c)=\max\limits_{x \in [a, b]} f (x) $ [on hold]

I saw in a corrected. We have $ f $ continuous on $ [a, b] $ with $ f (a) = f (b) $ and $ f $ differentiable left and right at $ (a,b)$ then $$ \exists c \in (a,b) \text{ such that } ...
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1answer
34 views

nth derivative of ${1\over x}$. A problem. [on hold]

$f(x)=f^{(0)}(x)=x^{-1}$, $f^{(1)}(x)=-x^{-2}$, $f^{(2)}(x)=2x^{-3}$. Therefore, $f^{(n)}(x)=(-1)^{n}n!x^{-n-1}$. Except I see in some places that the expression is different, using, for example, ...
1
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1answer
15 views

Proving that $\sup f'\left( \left( 0,\infty \right) \right)=0$ under a certain set of conditions.

Let $f$ be a twice differentiable function on $\left( 0,\infty \right)$ s.t. $f''(x)>0$ for all $x\in \left( 0,\infty \right)$. Prove, that if the following conditions are satisfied: ...
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0answers
19 views

Finding maximum of convex function (appliance of derivatives)

The task goes as following: Divide the length of $14$ into parts $a$ and $b$, in a way that the sum of surfaces of two squares (which sizes are $a$ and $b$), is minimal. $14=a+b => b=14-a$ ...
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0answers
22 views

Relationship between supremum of the partial derivative and the derivative of the supremum

To fully set up the problem: I have a function $$F : \mathbb R^n \times \mathbb R^+ \to \mathbb R$$ such that $F$ is positive and for any fixed $t^* > 0$, $$F(x,t^*) \in H^\infty(\mathbb R^n);$$ ...
2
votes
1answer
80 views

Derivative under integral mixed with…

$$f(x,y)=\int_{e^{4y}}^{\ln^3(x)}{\frac{\sin(t)}{t}\,dt}$$ Whats the derivative $\frac{d f}{d t}$, if: $$x(t)=\cos(2+6t).4t^2$$ $$y(t)=\ln(2r+7e^{5t})$$ Really not much to say about this problem ...
3
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3answers
49 views

Is the function complex differentiable at (0,0)?

(in Complex) $$ g(z) = \begin{cases} \frac{z^5}{|z|^4} & \text{if $z \neq 0$} \\ 0, & \text{if $z = 0$ } \end{cases} $$ For the function above, is it differentiable at $z=0$? I am trying to ...
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0answers
19 views

Differentiation through the integral sign, more general case

I wondered in which cases, given a measurable space $(A,\mu)$, Banach spaces $E,F$, an open $U\subseteq E$ and $f:A\times U\rightarrow F$, we can conclude that the function $s\mapsto\int_A f(x,y)dx$ ...
1
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1answer
47 views

${f \text{ is differentiable on } I \iff f_{\left|\ [a,b]\right.} \text{ is differentiable }\ \forall a,b \in I}$

Let $f\in \mathbb{R}^{I}$ $I$ interval of $\mathbb{R}$ Show that $${f \text{ is differentiable on } I \iff f_{\left|\ [a,b]\right.} \text{ is differentiable }\ \forall a,b \in I}$$ in ...
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1answer
86 views

Theorem $4.3.12$ on ( Mathématiques en BCPST Tome 1 Pascal BEAUGENDRE )

Let $f\in \mathbb{R}^{I}$ and $x_0 \in \stackrel{\ \circ}{I} = \mathrm{int}(A)$ Show that $$\left.\begin{matrix} f \text{ is continuous at } x_0 \\ f \text{ is differentiable at all } x \in I ...
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1answer
15 views

Derivative of a distribution

$\DeclareMathOperator{\vp}{v.p.}$ We define $\vp \frac 1x \in \mathcal D'(\mathbb R)$ (the principal value of $\frac 1x$) as $$\left\langle \vp \frac 1x, \varphi \right \rangle = \lim_{\varepsilon ...
1
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3answers
39 views

Find $f^{(n)}(1)$ where $f(x)={1\over x(2-x)}$.

Find $f^{(n)}(1)$ where $f(x)={1\over x(2-x)}$. What I did so far: $f(x)=(x(2-x))^{-1}$. $f'(x)=-(x(2-x))^{-2}[2-2x]$ $f''(x)=2(x(2-x))^{-3}[2-2x]^2+2(x(2-x))^{-2}$. It confuses me a lot. I know I ...
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6answers
137 views

Is $\sin^2(x)$ the same as $\sin x^2$?

I'm working with derivatives and need to know if $\sin^2(x)$ the same as $\sin(x^2)$? I almost don't want to ask because my last question was closed. It was a valid question and so is this one. I've ...
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1answer
16 views

Finding the stationary points of a function

I have a question that I need help with. How do I find the stationary points of the following function? $$y = \frac{4x^3}{(x-1)^2}$$ I differentiated the function and got $$\begin{align} y' ...
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1answer
16 views

Questions on continuously differentiable function on $[a,b]$

Let $f:[a,b]\rightarrow\mathbb{R}$ be a function. Normally we define derivatives of $f$ only at interior points in $[a,b]$. But when we write $f\in C^1([a,b])$, it means that $f$ is differentiable on ...
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1answer
23 views

Differentiability implies continuous derivative? [duplicate]

We know differentiability implies continuity, and in 2 independent variables cases both partial derivatives fx and fy must be continuous functions in order for the primary function f(x,y) to be ...
1
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2answers
24 views

Property of a differentiable function

Which one of the following is true: 1.If a function real valued function $f$ satisfies $|f(x)-f(y)|\leq |x-y|^{\sqrt2}$ for all $x,y\in \mathbb R$ is $f$ a constant? 2.If $f$ is ...
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0answers
21 views

Derivative of $Ad(c(t))X$

Let $G=SO(3)$ and $V=\{c'(0)|c:(-\epsilon,\epsilon)\to G, c\in C^{\infty} , c(0)=1\}$. For $g\in G$, define $Ad(g): V\to V$ by $Ad(g)(X)=gXg^{-1}$. The book says ...
0
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2answers
21 views

Numerical Approximation for 2D Curvature

I have a list of points (x, y) that are taken from an unknown 2D parametric curve $\vec{f}(t)$. These points are monotonically increasing in t (ie: they're a "connect the dots" version of ...
1
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4answers
75 views

Computing the sixth derivative of $F(x) = \int_1^x\sin^3(1-t)\mathrm dt$

Compute the sixth derivative at $x_0 = 1$ of $$F(x) = \int_1^x\sin^3(1-t)\mathrm dt$$ It's from a multiple choice test. I was able to narrow down the choices to $0$ and $60$. I guessed $0$ and ...
0
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1answer
548 views

Maximizing cross sectional area of trapezoid

The task is to fold a piece of sheet metal that measures 60 cm across in such a way as to form a trapezoidal "gutter" (a trough for carrying rainwater) with the maximum possible cross-sectional area. ...
1
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1answer
35 views

Is this theorem about integration with substitution wrong?

A theorem in my book states: If $g$ is differentiable, f is continuous, and F is an antiderivative of f, then : $\int f[g(x)]g'(x)dx=F[g(x)]+C$ The reason I am asking if this is correct, ...
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2answers
58 views

How to prove this equation about derivatives?

I'm currently studying derivatives, and I saw some equations but this one just not seems much trivial to me: $$\lim_{h\to 0}\left(\frac{f\left(x_0-2h\right)-f\left(x_0+3h\right)}{h}\right) = ...
2
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1answer
35 views

Differents between $lnx^2$ and $ln(x^2)$ Find derivative

I have this problem Find derivative for $lnx^2$. It seems that $lnx^2 \neq ln(x^2)$ since the derivative are differents using Wolfram Alpha. I don't understand how to calculate the derivative for ...
2
votes
2answers
50 views
+50

Is this proof that $g$ is continuous correct?

I have proved that $g$ is continuous on $(0,2)$ and I just wish to check if my solution for $g$ being right continuous at $0$ and hence continuous at $0$ is correct. $$\lim\limits_{x \to 0^+}g(x) ...
1
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1answer
17 views

nth derivative of a troublesome function

I don't know where to start on this problem. I'm trying to get the 2015th derivative(at x = 0) of f(x) = x^2 * arctan(x). Doing the derivatives one by one seems a little troublesome... What do you ...