Questions related to real and complex logarithms.

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2
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1answer
97 views

Calculate $I= \int_{1}^{e}\frac{(1+\ln x)x}{(1+x\ln x)^2}dx$

Please help me solve this: (level = high school) $$ \int_{1}^{e}\frac{(1+\ln x)x}{(1+x\ln x)^2}\,dx $$ Thanks
0
votes
1answer
23 views

What is the minimum degree of x so that it is greater than or equal to ln(x)?

I was thinking of this question and couldn't find it anywhere. I was trying to find a solution by finding the maximum of the function n = ln(ln(x))/ln(x) but I'm not sure if that's gonna work. Thanks ...
1
vote
1answer
35 views

Why does the same inequality give different answers?

$\left(\log _2\left(x\right)-2\right)\left(\log _2\left(x\right)+1\right)<0$ has a solution $\frac{1}{2}<x<4$ But when we take the second part alone that is $\left(\log ...
0
votes
1answer
38 views

Choosing a branch of the square root

Assume $O$ is the compliment of the non-positive part of the real line to the complex plane. This is an open and connected set. Only one of the values of $\sqrt z$ in $O$ has positive real part. With ...
1
vote
3answers
55 views

Convergence N'th Harmonic number minus the Natural Logarithm of N. [duplicate]

I was hoping if someone could show me the proof of exactly why this converges to the Euler–Mascheroni constant.
0
votes
3answers
88 views

How can I solve the following equation? [closed]

$\log_2{\frac{x-3}{x+2}}≤0$ Thank you.
-1
votes
2answers
123 views

How to show $\log_2 x \cdot \log_{0.25} x \cdot \log_{0.125} x \cdot \log_{16} x > \frac {2}3$?

I was trying to solve $\log_2 x \cdot \log_{0.25} x \cdot \log_{0.125} x \cdot \log_{16} x > \frac {2}3$ and I keep getting a partial answer of $x>4$ though answer key suggests a more expanded ...
0
votes
2answers
35 views

Simultaneous log equations

I'm going through logarithms at the moment, and I can't solve this simultaneous equation: $$\log x - \log 2 = 2\log y$$ $$x - 5y + 2 = 0$$ I've tried substituting both $x$ and $y$ to no avail: ...
2
votes
2answers
45 views

solving equations with powers

Im trying to solve the equation $$3\cdot2^{-2/x} + 2\cdot9 ^{-1/x} = 5\cdot6^{-1/x }$$ So far I tried applying logaritmas but it didnt prove helpful...are there any other ways?
1
vote
1answer
22 views

Using Stirling's approximiation to show that $(\log(\log n))!$ is $O(n^k)$

I am trying to show the following: Prove, using Stirling's approximiation, that $(\log(\log n))!$ is $O(n^k)$ for some positive constant $k$. Stirling's approximation is $$n!=\sqrt{2\pi ...
3
votes
1answer
68 views

Why $\ln(1)\neq 2\pi ik$

Given that $e^{2\pi ik}=1$ for all $k \in \mathbb{Z}$, why isn't $\ln{e^{2\pi ik}}=2\pi ik$? On the other hand $\ln(1)=0$. What am I missing here?
0
votes
1answer
48 views

How to simplify this equation? $1+\sqrt {2^{2a_{n}+b_{n}+1}-16^{a_{n}}-4^{b_{n}}}=\log _{3}\left( a_{n}+b_{n}\right) $

How to simplify this equation? $1+\sqrt {2^{2a_{n}+b_{n}+1}-16^{a_{n}}-4^{b_{n}}}=\log _{3}\left( a_{n}+b_{n}\right) $
0
votes
1answer
17 views

Solving Logarithms involving ceiling function

I need to solve the equation $\lceil \log_B(M) \rceil = S$ for $B$ when $M$ and $S$ are known, $M$ and $S$ are integers, and $B < M$. Were the ceiling function not there, it would be trivial, ...
2
votes
1answer
40 views

Name for a Logarithm Identity/Property

I came across a neat logarithm fact today: $\large n^{\log_bx} = x^{\log_bn}$ One simple proof is: $\large \log_bx\cdot \log_bn=\log_bx\cdot \log_bn$ $\large \Rightarrow ...
4
votes
5answers
70 views

What is the limit of $\log_k(k^a + k^b)$ for $k \to +\infty$?

I'm not very good with analysis (I never studied it) but because of my "work" on other topics of mathematics I came to this problem. $$\lim_{k \to +\infty }\log_k(k^a + k^b)=\max(a,b)$$ I'm sure ...
0
votes
3answers
61 views

Solve logarithmic equation: $2\log_7 (x+2) - \log_7 (3x+10) = 0$ [closed]

Please, can someone check if this is the right answer $$x= -2 \pm \sqrt{3x + 10}$$ Thank you.
2
votes
3answers
108 views

A series converging (or not) to $\ln 2$

I have come across the following series, which I suspect converges to $\ln 2$: $$\sum_{k=1}^\infty \frac{1}{4^k(2k)}\binom{2k}{k}.$$ I could not derive this series from some of the standard ...
3
votes
4answers
55 views

A general definition of Entropy (i.e. may or may not be expectation of the Log of the probabilities) [closed]

Entropy may be defined as Entropy = Σ G(p(x)) Where 'G' is any function that goes asymptotically to plus infinity as it approaches zero from the positive side and is monotonic between 0 and 1 ...
0
votes
2answers
51 views

Proof the expession $\log_{12}{18}*log_{24}{54} + 5(\log_{12}{18}-log_{24}{54})=1$

I am trying to proof the following expression (without a calculator of course). $\log_{12}{18}*\log_{24}{54} + 5(\log_{12}{18}-\log_{24}{54})=1$ I know this isn't a difficult task but it's just ...
1
vote
2answers
49 views

Definition of $a^b$ for complex numbers

Problem statement Let $\Omega \subset C^*$ open and let $f:\Omega \to \mathbb C$ be a branch of logarithm, $b \in \mathbb C$, $a \in \Omega$. We define $a^b=e^{bf(a)}.$ $(i)$ Verify that if $b \in ...
2
votes
1answer
36 views

How to solve this logarithmic equation?

I want to solve this equation: $$8n^2 = 64n\log_{\ 2}(n)$$ After some steps, I get to a point in which I believe, the only way to proceed is to apply something like Bolzano's or Newton's method to ...
2
votes
2answers
49 views

I need help on the process of solving this derivative.

How do I go about solving this derivative. $$f(x)=\ln\left(\frac{7x}{x+4}\right)$$ I go from this to $$1. \quad f(x)=\ln(7)+\ln(x)-\ln(x+4)$$ and then $$2. \quad f'(x)=\frac{1}{x}-\frac{1}{x+4}$$ then ...
2
votes
2answers
86 views

How do I simplify $\log (1/\sqrt{1000})$?

How do I simplify $\log \left(\displaystyle\frac{1}{\sqrt{1000}}\right)$? What I have done so far: 1) Used the difference property of logarithms $$\log ...
0
votes
2answers
41 views

Help me solve this…

Assuming $a=\log 2$ and $b=\log 3$ (log is the base 10 logarithm). I have to find $\log_5 288$. How can I do this? Edit: I've tried transforming $\log2$ to $\frac{\log_5 2}{\log_5 10}$ and same for ...
5
votes
3answers
172 views

Help with logarithmic definite integral: $\int_0^1\frac{1}{x}\ln{(x)}\ln^3{(1-x)}$

I'm look for a closed form evaluation of the following improper definite integral involving logarithms: $$\begin{align} I:&=\int_{0}^{1}\frac{1}{x}\ln{(x)}\ln^3{(1-x)}\,\mathrm{d}x\\ ...
0
votes
0answers
24 views

Using math functions to time finales of a fireworks show

This year, I have the honor of programming two finales for a fireworks show. I want to use math. I suspect that I should use a function such as square root or log to specify the decreasing pause ...
0
votes
1answer
11 views

Consumption change calculation

I want to calculate yearly consumption change according to the following formula: $$C_{t+1}=C_{t}e^{x_{t}}$$ I need to calculate ${x_{t}}$. I have the consumption data $C_{t+1}$ and $C_{t}$.
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votes
2answers
47 views

How to get this answer [closed]

Anyone help me solve this question $$\ln u + 2 \ln(1-u) - 2 \ln(1+u) = 2 \ln x + \ln c$$ I have the answer as $\frac{x y}{ (x^2 - y^2)^2} =c$, but I cant figure out how get this answer.
2
votes
1answer
29 views

Does $\sum_{i=1}^{k-1}\lceil \log_2\frac{N}{i}\rceil$ have a closed form?

Does the following have a closed formula? $$\sum_{i=1}^{k-1}\left\lceil \log_2\frac{N}{i}\right\rceil$$
7
votes
3answers
192 views

Is $ln(x)$ ever greater than $x$

Is $\forall x \in \mathbb{R}, \ln(x) \lt x$ a true statement? Just wondering for some convergence related thing
2
votes
1answer
71 views

Checking derivation of y = a^x

Can you tell me if there are any flaws with this derivation of $y = a^x$... The assumptions are that the derivative $$\frac{d}{dx}e^x = e^x$$ and that the derivative $$\frac{d}{dx}\ln x = ...
0
votes
1answer
43 views

Is there a property for log(n)/n?

I found a small exercise which I couldn't figure what to do, so I found a solution. Then I tried to understand it and everything went well until I got to this part: $$\frac{1}{8} = ...
0
votes
2answers
51 views

Help me to solve math homework on logarithmic

How to solve this math home work? Please help.. What is the value of $\log \left(\dfrac{i\pi}{2}\right)$ ? I got to know the answer is "$\dfrac{i\pi}{2}$", but don't know how to solve it. Please ...
1
vote
3answers
41 views

If $2 \cdot log_e{(x -2y)} = log_e{y} + log_e{x}$, then find the numerical value of $\frac{x}{y}$

If $2 \cdot log_e{(x -2y)} = log_e{y} + log_e{x}$, then find the numerical value of $\frac{x}{y}$ My try: $2 \cdot log_e{(x -2y)} = log_e{y} + log_e{x}$ $log_e{(x-2y)^2} = log_e{xy}$ ...
0
votes
1answer
27 views

Mathematics - geometric progression question

If $a$, $b$ and $c$ are in geometric progression, then what are $\log_ax$, $\log_bx$ and $\log_cx$ in? What I did: I substituted values for $x, a, b$ and $c$ and tried to solve it further. What I ...
2
votes
1answer
57 views

What does this log notation mean?

Can someone please explain what $^2\log x$ means? Is it the same as saying $\log x^2$ or is it something completely different? Here is an image of it as an example:
0
votes
0answers
32 views

characteristic function of logarithm of random variable

If I know the characteristic function $\phi_X(t)$ of a random variable $X>0$, how can I write the characteristic function $\phi_Y(t)$ of $Y=\log(X)$? I know that $\phi_X(t)=E[e^{itX}]$ and ...
6
votes
1answer
170 views

$\exp(\ln(x))=x$ and $\ln(\exp(y))=y$.

Let $(A,1_A,|\cdot{}|)$ be a unital Banach algebra, for instance $A=M_n(\Bbb R)$ or $M_n(\Bbb C)$. What is the union of all open unit balls $B_{\|\cdot{}\|}$ where $\|\cdot{}\|$ ranges over all ...
0
votes
1answer
24 views

How to define this logarithmic function

I am trying to get my head around the definition of this function (that I concocted as an exercise in defining a function). Let $f$ denote the function satisfying: $f(0) = +\infty$, and $f(+\infty) = ...
0
votes
1answer
47 views

Show that $\frac 1{\log_2x}+\frac 1{\log_3x}+\cdots+\frac 1{\log_{43}x}=\frac 1{\log_{43!}x}$ [closed]

Show that $\frac 1{\log_2x}+\frac 1{\log_3x}+\cdots+\frac 1{\log_{43}x}=\frac 1{\log_{43!}x}$.I am just not able to get it.please help.
0
votes
2answers
22 views

definition or property of logarithms

I've seen a lot of complicated logarithm definitions on this StackExchange and I have a rather simple question: $$a^{b}=c \leftrightarrow \log_a{c}=b$$ Is this a definition of logarithms, which all ...
0
votes
2answers
37 views

Logorithms on a first level learning

Solve log$_{5x-1}$ $4$ $=$ $1/3$ $(5x-1)^{1/3}$=4 $((5x-1)^{1/3})^3$ = $4^3$ $5x-1=64$ $5x=65$ $13$ I am not sure where to go with this. I learned some things about logs before my class ended ...
0
votes
3answers
74 views

Question releating to the $\int^x_1\frac{\ln(t)}{t+1}$

If $f(x)=\int^x_1\frac{\ln(t)}{t+1}dt$ if $x > 0$. Compute $f(x) + f(1/x)$. As a check, you should obtain $f(2)+f(1/2)=(\ln2)^2$ I have tried evaluating the integral ...
2
votes
0answers
35 views

Interpolation of iterated logarithms

$$\text{Let }\log^2(x)=\log(\log(x)),\\ \text{ then }f(y,x)=\log^{\lfloor1+y\rfloor}\left(\log(x)/\log((1-x^{1/x}(y-\lfloor y\rfloor))+(y-\lfloor y\rfloor))\right)$$ gives an interpolation between ...
3
votes
3answers
80 views

calculate $\int_{0}^{\pi} \int_{0}^{x}\log(\sin(x-y))dydx$

I was asked to find the integral $\iint_A \log(\sin(x-y))dxdy$ where $A$ is the triangle $y=0, x=\pi, y=x$ in the first quadrant. I was given a hint: evaluate $\int_{0}^{\pi}\log(\sin(t))dt$ using ...
1
vote
1answer
45 views

$\sum_{x=a}^{b-1}\frac{1}{x}$ and $\sum_{x=a+1}^b\frac{1}{x}$

I have to prove the following relations: $\sum_{x=a}^{b-1}\frac{1}{x}\geq\log b - \log a $ $\sum_{x=a+1}^{b}\frac{1}{x}\leq\log b - \log a $ I tried to use the relation that $\int_a^b \frac{1}{x} ...
0
votes
3answers
32 views

Logarithm deduction question

Given that $\log_{10}2 = 0.3010$ to four decimal places and that $10^{0.2} < 2$, is it possible to deduce that: $2^{100}$ begins in a $1$ and is $30$ digits long; $2^{100}$ begins in a $2$ and is ...
0
votes
1answer
41 views

How to calculate arithmetic mean of log values

I am working with really small values of probabilities and that is why their log values are used. So for example, let probA and probB be some normal values of probabilities of two events and because ...
1
vote
1answer
31 views

Help with Evaluating a Logarithm

A precalculus text asks us to evaluate $\log_{8}\dfrac{\sqrt{2}\cdot\sqrt[3]{256}}{\sqrt[6]{32}}$ I do the following: $\log_{8}\dfrac{\sqrt{2}\cdot\sqrt[3]{(2^2)^3\cdot 2^2}}{\sqrt[6]{2^3\cdot 2^2}}$ ...
1
vote
3answers
51 views

Determine all positive numbers $a$ for which the curve $y = a^x$ intersects the line $y = x$ without calculus

The answer is $0 < a < e^{1/e}$ , but how to find it? Is it a system of equations? Which ones? I just need an idea at least, because I'm stuck. If it is impossible without calculus, solve it ...