Questions related to real and complex logarithms.

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2
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0answers
110 views

Is this equal ? (I found it on this website)

I found this equation on this website! I would like to know it its true or not? And how can proof or disprove it?! Euler-Mascheroni constant expression, further simplification ...
1
vote
1answer
10 views

Find all solutions for a complex logarithm

$\log z = 6i$ I am working on a problem very similar. What I am seeing $\log z = \ln|z| + i(\theta + 2\pi n)$ for $n\in\mathbb{Z}$ What I am curious about, as if seen obvious to me that $ \log ...
0
votes
0answers
85 views

How can we proof that this is equal? About $ln(n)$

I found this on this website (Euler-Mascheroni constant expression, further simplification) without any explaining why this is equal can someone give me that? ...
3
votes
2answers
100 views

Is $g(x)=\log x$ convex function?

The graph of convex function is : In a book it is written that $g(x)=\log x$ is strictly convex function. So i searched for graph of $g(x)=\log x$ and found that Though it has been said that ...
1
vote
0answers
41 views

Analytically solving complicated integral involving logarithms.

I already asked a similar question a week ago and the comment I got helped me a lot with my progress, so that I now have new question to ask. I am stuck with solving a complicated integral and would ...
0
votes
2answers
45 views

Different results when integrating $1/(x \ln(x))$ partially/by substitution.

By substitution I get $ln(ln(x))$. Partially something completely different: $$\int \frac{1}{x \ln(x)} = \int \frac{1}{x} \frac{1}{\ln(x)} dx=\frac{\ln(x)}{\ln(x)} - \int -\frac{1}{x \ln(x) ^2} dx$$ ...
4
votes
1answer
307 views

inequality $10<2^{2^{\frac {3}{\log_2 \log_2 10}}}$

While working on this question I ended up with $10<2^2{^{\frac {3}{\log_2 \log_2 10}}}$ I am looking for answers using methods similar to this or this or this or this. Alternative original ...
0
votes
1answer
53 views

A Trig Integral

Does the integral \begin{align} \int_{0}^{\pi/2} \cos(x) \, \ln\left( \frac{1 + a^{2} \sin(x)}{1 - a^{2} \sin(x)} \right) \, dx \end{align} have a closed form and what is changed if the limits are ...
22
votes
2answers
629 views

Integral $\int_0^1\frac{\ln x}{x-1}\ln\left(1+\frac1{\ln^2x}\right)dx$

Is it possible to evaluate this integral in a closed form? $$ I \equiv \int_{0}^{1}{\ln\left(x\right) \over x - 1}\, \ln\left(1 + {1 \over \ln^{2}\left(x\right)}\right)\,{\rm d}x $$ Numerically, ...
6
votes
3answers
339 views

Definite integral involving logarithm of cosine

Does anyone know the provenance of or the answer to the following integral $$\int_0^\infty\ \frac{\ln|\cos(x)|}{x^2} dx $$ Thanks.
1
vote
2answers
28 views

Prove the logarithmic inequality

Prove that: $(\log_{24}{48})^2+(\log_{12}{54})^2>4$ I tried to put $t=\log_23$ and get the equation $6t^4+32t^3+22t^2-84t-74>0$. But I can't do anything with it...
1
vote
1answer
49 views

Inequality with Logarithms!

I need some help solving this inequality for a question involving the number of bounces, $n$, of ball such that the max. height of the ball is less than 5cm. This is the equation I have gathered from ...
2
votes
1answer
53 views

A definite integral contianing ln(x)

everyone, I met a tough definite integral as follows, $$I = \int\limits_1^\infty {\frac{{\ln x}}{{{{\left( {x + a} \right)}^m}{{\left( {x + b} \right)}^{n + 1}}}}} dx,$$ where $a$ and $b$ are ...
0
votes
1answer
36 views

Complex logarithm function

I need some help understanding the logarithm function in complex plane. Let $w,z\in \mathbb{C}$. Define $$w=e^z$$ when $$z=\log(w).$$ Now I understand the representation of ...
1
vote
1answer
43 views

Solving Log equation using master theorem

I`m studying Master Theorem, and I got stuck in the case 3. The example is : T(n) = 3T(n/4) + nlogn. I have no idea how my teacher got the final value, c = 3/4, based on the equation below : 3*[n/4 ...
1
vote
1answer
67 views

Simplifying a log of a log

I have a summation series that unfortunately involves a log of a log. It looks like the following (assume all $\log$ are log base $2$): $$ \sum_{i=1}^k \log\log\frac{n}{2^{k-i}} $$ I'd like to ...
-4
votes
2answers
261 views

For what $n$ does $[\log_21]+[\log_22]+[\log_23]+\dotsb+[\log_2n] = 1538$? [duplicate]

I just can't solve this problem in spite of doing a whole book on logs and inequalities Where $[\dotsc]$ denotes the greatest integer function, what is the value of the natural number $n$ ...
1
vote
2answers
47 views

$\sum x^n/n$ — why does it equal $\log(\frac {1}{1-x})$?

Define the function $D(x) = x + x^2/2 + x^3/3 + \cdots$ I found out during a brief exchange with a friend that this sum equals $\log\left(\frac 1{1-x}\right)$ for $|x| < 1$. He had learned it in a ...
0
votes
2answers
49 views

An equation not so easy! Help me with this logarithmic equation!

I need help with the following problem analysis, if someone could I resolve all steps. Let $a>0$. Determinate the number of solutions of the equation $ax^2 = \log x$, according to the values the ...
0
votes
1answer
17 views

Solving exponential equation - Order of operations

Hopefully this should be a quick questions. When solving the exponential equation 5 * 2^(u/2) + 30 = 600 Why do you subtract 30 first and not divide 600 by 5? The order of operations indicates that ...
0
votes
2answers
28 views

Verify that Log$(z^{w}) = w$Log$z$ + $2\pi i n$

The symbol "Log" denotes the complex logarithm. Let $w$ be a complex number so that $w = u+iv$ for some reals $u, v.$ We have $$\mbox{Log}(z^{w}) = \log |z^{w}| + i\arg (z^{w}) = u\log |z| - v\arg ...
11
votes
3answers
553 views

How was the first log table put together?

Henry Briggs compiled the first table of base-$10$ logarithms in 1617, with the help of John Napier. My question is: how did he calculate these logarithms? How were logarithms calculated back then? ...
0
votes
2answers
29 views

Help to find the best lower bound function for a given set of data, based in the natural logarithm function

I am trying to find a lower bound function for a set of data I have, and I am struggling with it. In the following graph the blue color is the set of data and the red color is my lower bound function. ...
0
votes
2answers
45 views

Tricky Logarithmic Inequality Problem

I am having a problem solving this question - If $\log_{\frac{1}{\sqrt{2}} }{\sin{x}}>0$, $x\in [0,4\pi]$,then number of values for chating which are integral multiples of $\pi/4$,is A-6 B-12 ...
2
votes
3answers
69 views

Integral of $\log(\sin(x)) \tan(x)$

I would like to see a direct proof of the integral $$\int_0^{\pi/2} \log(\sin(x)) \tan(x) \, \mathrm{d}x = -\frac{\pi^2}{24}.$$ I arrived at this integral while trying different ways to evaluate ...
1
vote
0answers
22 views

Taking integral of the complex logarithm using fundamental theorem?

Is it valid to do this? I have $f(z)= z^i$,and $F(z)=\frac{z^{i+1}}{i+1}$ and assuming we're using principle values of $f$ and $F$ would it be correct to say that: $\int_{-1}^{1} f(z) dz = ...
1
vote
1answer
49 views

Fourier transform and splitting frequency range into 4 channels

I have code example that divides audio frequency into 6 channels. It uses Fast Fourier Transform (FFT). Algorithm process the frequency range using 6 capture[x] samples based on the range of n between ...
0
votes
1answer
35 views

Minimum value of a Logarithmic equation

What is the minimum value of $$\log_a(x)+ \log_x(x) $$ where $0\leq a\leq x.$ I do not understand why my book says the answer is $2$ because when i take $a=0.1$ say and $x =0.2$ I get $\approx ...
2
votes
0answers
25 views

Asymptotic solution to $m \leqslant e^{\lambda t} (c t^q - \varepsilon)$

What is the smallest $t$ statisfying the inequality: $m \leqslant e^{\lambda t} (c t^q - \varepsilon)$, where $\varepsilon$ is arbitrary small positive number? I believe $t$ must be of the from: $$t = ...
0
votes
1answer
42 views

Logarithmic question

In the following question I fail to understand why the A option is correct. I understand that D is wrong, and that B and C are correct, but why is A correct? If $3^x=4^{x-1}$, then $x $cannot be ...
1
vote
2answers
39 views

Determine the convergence or divergence of $\sum_{2}^{\infty}\frac{1}{(\log n)^{s}}$, where $s \in \mathbb{R}$ is given.

Since $$\frac{1}{(\log n)^{s}} > \frac{1}{n^{s}}$$ for large $n$, if $s \leq 1$ then $\sum_{2}^{\infty}\frac{1}{(\log n)^{s}}$ diverges. But for $s > 1$ I have not yet figured out a proof.
-2
votes
2answers
118 views

Can anyone solve this equation? [on hold]

Having trouble working this one out: $$25^x + (2 .5)^x = 35$$ Any help would be appreciated.
0
votes
0answers
27 views

Taking the logarithm of a periodic function

I've been wondering how we take the logarithm of a periodic function. At least I think that's what I've been wondering - but I may have confused the terminology. Anyway, take, for example, the ...
0
votes
2answers
51 views

Is it true that $\int_{0}^{1}(1+x^{2})^{-1/2} = \log (1 + \sqrt{2})$?

Since $$D^{-1} (1 + x^{2})^{-1/2} = \sinh ^{-1} (x) + C,$$ is it true that $$\sinh ^{-1} x + C \big|_{0}^{1} = \log (1 + \sqrt{2})?$$ What relates $\sinh^{-1}(\cdot )$ to $\log(\cdot )$? Here ...
-1
votes
2answers
34 views

Integration of logarithm

$\int \ln(\ln \sqrt{x})^{\ln (x)}dx$ how should I integrate this? I think it can't be integrated. I don't know.
1
vote
1answer
17 views

The position of significant digits and Logarithms relationship…

I am unable to solve the following question has i don't understand what the relationship is between significant figures and Logarithms. Q-If $\log_{10}(7)= 0.8451$ then the position of the first ...
2
votes
1answer
29 views

Stuck with understanding transformation step in calculating limit of $n(\sqrt[n]{a}-1)$

Although this question has already been asked in general ( $\lim\limits_{n\to\infty} n·(\sqrt[n]{a}-1)$) , my question is different, because I am stuck with a specific transformation step: ...
0
votes
2answers
52 views

What is this equation?

I ran across this equation for use in web code here and am desperately wanting to know if any portion of it or the whole thing is a standard equation somewhere. This is the best I could do ...
0
votes
2answers
36 views

rewrite logarithmic expression

I have this logarithmic expression 2 logb 6 + (1/2) logb 25 - logb 30 and have to rewrite it as logb of one number. I just don't understand how to do this. help please.
1
vote
1answer
32 views

How to prove that $f(x) = x^ε - \log x$ is $\infty$ when $x\to\infty$?

I'm trying to prove that the function $x^ε$ is "bigger" than $\log x$ when $x\to\infty$, for every $ε>0$. Or to put it in a more formal way: For every $ε>0$, there exists a constant $N$ for ...
0
votes
1answer
33 views

Simplification of a logarithm expression

I need to verify the answer of a logarithm expression (note, I'm not a student). I managed to get through high school and college without ever having a math course that taught logarithms--I don't ...
0
votes
1answer
20 views

Deriving a function with logarithmic terms

Let $L(X) = \exp(\sqrt{\log X \log \log X})$ Prove that if $c > 0$,$ Y = L(X)^c$, and $u = \log X/ \log Y$ , then $$u^u = L(X)^{(1/2c)(1+o(1))}$$ I've tried to write $u^u = (\log X/ \log ...
1
vote
1answer
31 views

Logarithm, Just need help understanding what this question is asking. Not looking for an answer.

In my foundations of computing class, we were given a logarithm question which i don't quite understand. This is the question. Given the logarithmic table values of the numbers x and y are ax and ay ...
27
votes
2answers
909 views

Are there other cases similar to Herglotz's integral $\int_0^1\frac{\ln\left(1+t^{4+\sqrt{15}}\right)}{1+t}\ \mathrm dt$?

This post of Boris Bukh mentions amazing Gustav Herglotz's integral $$\int_0^1\frac{\ln\left(1+t^{\,4\,+\,\sqrt{\vphantom{\large A}\,15\,}\,}\right)}{1+t}\ \mathrm ...
27
votes
3answers
662 views

Integral $\int_0^1\frac{\ln x}{\left(1+x\right)\left(1+x^{-\left(2+\sqrt3\right)}\right)}dx$

There is a curious known integral: $$\int_0^1\frac{\ln\left(1+x^{2+\sqrt{3\vphantom{\large3}}}\right)}{1+x}dx=\frac{\pi^2}{12}\left(1-\sqrt{3\vphantom{\large3}}\right)+\ln ...
1
vote
2answers
50 views

Deriving properties of the logarithm from its integral representation

Suppose we define: $$\ln(x) = \int_{a}^{x} \left[ \frac{1}{r} dr\right]$$ Such that $$ \ln(1) = 0, \ln(e) = 1$$ How does one derive all the properties of the logarithm from the properties of the ...
0
votes
6answers
62 views

Limit of log functions

I need help solving this problem. $$\displaystyle \lim _{x\to 0}\frac{\log\left(1+7x\right)}{5x}$$
-4
votes
1answer
75 views

Check whether a function is one-to-one and onto

If $f(x) = \log_{x^3}\left(\sqrt{x}\right)$, check whether $f$ is one-to-one and onto where $x\in R^+\setminus\{1\}$. Also write the range of $f$. Alright, if $f(m) = f(n)$ and if we would prove m=n ...
3
votes
1answer
97 views

Log or Antilog tables, which ones are more useful?

I'm trying to make a Log or Antilog table small enough to fit in the back of a wallet calendar (or a business card). My intend is to build a mathematically useful gift that can be used by anybody ...
1
vote
1answer
29 views

proving with a sequence

The question is : Show that if $n$ is a power of $2$, then $$\sum_{i=0}^{\log_2n-1}2^i=n-1\;.$$ Tried induction at first and tried to prove it on 2n but nothing came out of it. Then i tried ...