Questions related to real and complex logarithms.

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1
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2answers
44 views

Natural log operation on $e^{i \tau}$ [duplicate]

I have a layman's question: $e^{i\pi} = -1$ ... euler's identity and $e^{i\tau}$ = 1 where $\tau = 2\pi$ so if I assume that $e^x=y$ implies $ln(y)=x$, which it should, then $ln(1) = i\tau$ but $...
1
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2answers
34 views

Solve the equation $2^{x^2 + x} + \log_2x=2^{x+1}$

Solve the equation $2^{x^2 + x} + \log_2x=2^{x+1}$ where $x$ is real. I tried to use derivatives, without success. It's obvious that $x=1$ is solution. Also, if $x \gt 1$ then $2^{x^2 + x} \gt 2^{...
1
vote
0answers
41 views

How do I solve this tricky logarithmic formula

I have a formula as follows: $0.55508389365 = \ln(20 + x)/\ln(240 +x)$ I happen to know that x = 1 (approximately) is the solution. But I'm not sure how I would go about solving this if I didn'...
0
votes
2answers
84 views

Prove that $\log(n!)\leq(\log(n))!$

Prove that $\log(n!)\leq(\log(n))!$ My attempt: I read somewhere that $n\leq\log(n!)\leq(\log(n))!$. But when I used calculator $\log(n!)$ can not be less than or equal to $(\log(n))!$. ...
7
votes
1answer
180 views

Convexity of difference of log-sum-exp: $f(x_1, x_2, x_3, x_4) = \log(e^{x_1} + e^{x_2}) - \log(e^{x_1} + e^{x_2} + e^{x_3} + e^{x_4})$

I would like to know whether the following function $f: \mathbf{R}^4 \to \mathbf{R}$ is concave or not: $$ f(x_1, x_2, x_3, x_4) = \log(e^{x_1} + e^{x_2}) - \log(e^{x_1} + e^{x_2} + e^{x_3} + e^{x_4})...
1
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0answers
48 views

What is the most important purpose of the $\log$ function?

I read somewhere that the most important purpose of the $\log$ function is that it provides an antiderivative of $1/x$. I thought $\log$ was defined and is most widely used to deal with exponential ...
1
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2answers
96 views
+100

$\log(e^z - i)$ as a holomorphic function in $\mathbb{D}$

I'm learning complex analysis, specifically holomorphic functions, and need help with the following exercise: Examine if the function $\log(e^z - i)$ can be defined as a holomorphic function in ...
3
votes
1answer
42 views

logarithm of a sum or addition

I search a general rule for calculating the logarithm of a sum or addition. I know that $$\ln{(a+b)}=\ln{\left(a\left(1+\frac b a\right)\right)}=\ln{(a)}+\ln{\left(1+\frac b a\right)}$$ but when the ...
0
votes
0answers
7 views

Estimate the complexity for number times the function n/ lgn will be called recursively such that the result is a constant c = 2?

Cormen exercise $3.6$ which defines recursive function $f(i)$ such that $i$, $i \ge 0$ and the function is recursively called on itself $f(….f(i))$ such that it reaches a constant $c= 2$. Please help....
1
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2answers
30 views

Why is it true that $S'(t)/S(t) = d log(S(t)) / dt$?

I came across this identity in derivation of the hazard rate in survival analysis.
1
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1answer
25 views

If $x(z)$ and $y(z)$ are analytic with $x(0) = 0 = y(0)$ then $x(z)^{y(z)} \to 0$ as $z \to 0$

I'm a programmer and my math is a little rusty, but usually sufficient for my needs. However, I came across the following statement in the exp(3) manual page of ...
0
votes
2answers
54 views

Logarithmic equation's solution [on hold]

I'm unable to solve this equation further. Could someone have a shot at it and try to solve it and explain it to me please? The equation is $$2\log_{2}(\log_{2}(x))-\log_{2}(\log_{2}2\cdot 2^{0.5}x)=...
-1
votes
1answer
80 views

How to solve $\log_2(x) +3 = \log_3(x+2)$ [on hold]

Hi Math Stack Exchange Communities, I am new here. I have a question regarding logarithm solving. Let's say I have this equation: $$\log_2 (x) +3 = \log_3 (x+2)$$ How can I solve this kind of ...
0
votes
3answers
41 views

How to simplify the expression $(\log_9 2 + \log_9 4)\log_2 (3)$

Our test asked to simplify $(\log_9 2 + \log_9 4)\log_2 (3)$. I simplified the first parenthesis to be $\log_9 (8)$. So, now I have $\log_9 (8) \cdot \log_2 (3)$ and I can change to base $10$ and ...
1
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3answers
3k views

how to get value of n if the value of n * log n is given? [duplicate]

Possible Duplicate: How can I solve for $n$ in the equation $n \log n = C$? how to get value of n if the value of n * log n is given ? I am stuck with this: ...
6
votes
0answers
139 views

Integral ${\large\int}_0^{\pi/2}\frac{x\,\log\tan x}{\sin x}\,dx$

Could you please help me to find closed form expressions for the following definite integrals: $$I_1=\int_0^{\pi/2}\frac{x\,\log\tan x}{\sin x}\,dx\approx0.3606065973884796896...$$ $$I_2=\int_0^{\pi/3}...
2
votes
2answers
49 views

For which values of $a$ does $d\ge ac\ln c\implies d\ge c\ln d$?

For which values of $a>0$ is it true that for all $c,d>0$, $\hspace{.2 in}d\ge ac\ln c\implies d\ge c\ln d$? I believe that this is true for $a\ge2$, (see Showing if $n \ge 2c\log(c)$ then $n\...
2
votes
1answer
31 views

How to rigorously deduce the Laurent series of $\log\frac{z-p}{z-q}$?

Of course, the logarithm here is defined on the ring region $|z|>R\ge\max\{|p|,|q|\}$ as $$\log\frac{z-p}{z-q}=\int_{z_0}^z \left(\frac1{w-p}-\frac1{w-q}\right)\mathrm d w. $$ Here the integral is ...
4
votes
3answers
158 views

$2^n=n$ and similar equations

Is it possible to solve equations in the form $k^n=n$ for n and if so, How? I am new to logarithms and so would be glad if someone could explain even if there is an obvious answer. Also What about $k^...
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votes
1answer
52 views

What would $\log_{24} 48$ be in terms of $x$ if $\log_{12} 36= x$? [on hold]

What would $\log_{24} 48$ be in terms of $x$ if $\log_{12} 36= x$? Which properties to use and how to proceed, please let me know.
0
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1answer
61 views

Problem on logarithm

$$\mbox{If}\ \log_{2a}\left(a\right) = x,\ \log_{3a}\left(2a\right) = y,\ \log_{4a}\left(3a\right) = z.\quad \mbox{Then, what is the value of}\ xyz-2yz\,?. $$ Not exactly able to solve it any further.
0
votes
1answer
33 views

Logarithmic equation solution

If $ \frac {\log a}{b-c}=\frac{\log b}{c-a}=\frac{\log c}{a-b}$,then what would be the value of $a^{b+c}.b^{c+a}.c^{a+b}$? I'm unable to proceed.
0
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3answers
52 views

question from logarithms [on hold]

Simplify without using tables $$\frac{\log25+\log625}{\log5}$$
3
votes
4answers
52 views

Find $\lim_{n\to\infty}\ln(n^{n}\cdot(n+1)^{-n-1})$

I have to solve this limit: $$\lim_{n\to\infty}\ln(n^{n}\cdot(n+1)^{-n-1})$$ I know the answer is $-\infty$. My question is, can I do this: $$\ln[\lim_{n\to\infty}n^{n}\cdot(n+1)^{-n-1}]$$ If not, how ...
2
votes
2answers
113 views

Formula for proportion of entropy

Let's say we have a probability distribution having 20 distinct outcomes. Then for that distribution the entropy is calculated is $2.5$ while the maximal possible entropy here is then of course $-\ln(\...
-5
votes
1answer
42 views

it is a logarith question $25(2^{\log x}) = x$ [closed]

$$25(2^{\log x}) = x$$ We need to find for $x$ 25(2^logx) = x 100÷4(2^logx) = x 100(2^logx) = x 10^2(2^logx) = x 10^log100(2^logx) = x. PLEASE FINISH OR DO IT IN YOUR OWN WAY
0
votes
1answer
75 views

$\log_5 {(x+1)} - \log _4 {(x-2)} = 1$

I tried to solve this equation by changing bases. $\dfrac {\log_4 (x+1)}{\log_4 5} = \log_4 (4x -8)$ $.86 \log_4 (x+1) = \log_4 (4x-8)$ Then i got stuck. Please share your idea with me.
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2answers
39 views

Defining logarithms explicitly

How are logarithms defined explicitly? One way I can come up with is the following, first start by using McLaurin series representation of exponent function: $$e^x = \sum_{k=o}^{\infty}\frac{x^k}{k!}...
1
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2answers
62 views

How to solve for log with a number outside?

$$\log_6(4x-10)+1 = \log_6(15x+15)$$ This is a sample problem. I know that when the bases of log are the same, all you have to do is set the parenthesis inside equal to each other. If the $1$ wasn't ...
0
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2answers
51 views

Calculate $\log_{\frac{1}{2}}{(2\sqrt[3]{4})}$

I have this exercise:$$\log_{\frac{1}{2}}{(2\sqrt[3]{4})}$$ There is not equation or something else, how should I solve this type of exercise?
0
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2answers
49 views

$e^{e^{10^{10^{2.8}}}}$ changing $e$ with $10$

From Numberphile $$e^{e^{10^{10^{2.8}}}}$$ changing $e$ with $10$, is there a way to change only the top most number while keeping all other numbers 10? i.e what is x in : $$e^{e^{10^{10^{2.8}}}} = ...
2
votes
2answers
34 views

Solve the following (logarithmic) function for x

$x^{log_{2}x}+16x^{-log_{2}x} = 17$ Looks horrible, I started by removing the exponents: $e^{ln(x)*log_{2}x}+16e^{-ln(x)*log_{2}x}=17$ | ln() $ln(x)*log_{2}x-16ln(x)*log_{2}x=ln(17)$ $ln(x)*log_{...
20
votes
7answers
7k views

Computing the integral of $\log(\sin x)$

How to compute the following integral? $$\int\log(\sin x)\,dx$$ Motivation: Since $\log(\sin x)'=\cot x$, the antiderivative $\int\log(\sin x)\,dx$ has the nice property $F''(x)=\cot x$. Can we ...
2
votes
2answers
42 views

Solve the following (logarithmic) function for $x$

$(\log_{3}x)^{2} - 3\log_{3}x + 2 = 0$ We may not use many rules, so I would start by ignoring the ^(2), ignore -3* but take ...
1
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0answers
7 views

Caclulate Standard Error when subtracting two effects

I am working on this issue that compares two regions with the McCrary Test (Regression Discontinuity Design). It basically measures how the density of a variable of interest develops accross a pre set ...
1
vote
1answer
33 views

Question about distribution of primes

The following is from "Introduction to Number Theory" by Hardy and Wright. The book first states the following theorem Theorem A: If $\pi(x)$ is number of primes not exceeding $x$ then $\pi(x) \...
5
votes
2answers
95 views

Finding Limit of Nested/Continued Logarithm

For a sequence $a_n$ defined by: $$a_1 = \ln(1)$$ $$a_2 = \ln\left(\frac{1}{\ln(2)}+1\right)$$ $$\dots a_n = \ln\left(\frac{1}{\ln(\frac{1}{\ln(\dots 1/\ln(n ))}+1)}+1 \right)$$ with $n$ ...
2
votes
6answers
132 views

Solve equations like $3^x+4^x=7^x$

How can I solve something like this? $$3^x+4^x=7^x$$ I know that $x=1$, but I don't know how to find it. Thank you!
10
votes
4answers
263 views

Evaluating $\int_{0}^{\pi}\ln (1+\cos x)\, dx$ [duplicate]

The problem is $$\int_{0}^{\pi}\ln (1+\cos x)\ dx$$ What I tried was using standard limit formulas like changing $x$ to $\pi - x$ and I also tried integration by parts on it to no avail. Please help....
1
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0answers
54 views

If the last term of $(2^{1/3}-\frac{1}{\sqrt{2}})^n$ is $(\frac{1}{3^{5/3}})^{\log(\frac{8}{3})}$, what is the $5\rm{th}$ term from the beginning? [closed]

If the last term of $$\left(2^{1/3}-\frac{1}{\sqrt{2}}\right)^n$$ is $$\left(\frac{1}{3^{5/3}}\right)^{\log(\frac{8}{3})}$$ then the value of $5th$ term from beginning is ?. So I simplified $(243)^{1/...
3
votes
1answer
37 views

How can I prove this inequality involving logarithm?

$n^2 \geq n \log_{2}n$ I tried like this: $n^2 \geq n \log_{2}n$ $n^2-n \log_{2}n \geq 0$ $n(n-\log_2 n) \geq 0$ I don't know what to do after this?
2
votes
4answers
97 views

If $\ln(1+x) \approx A+Bx+Cx^2$, differentiate twice both sides and show that $\ln(1+x) \approx x-\frac{1}{2}x^2$

Question: $\ln(1+x) \approx A+Bx+Cx^2$, for $-1<x\leq1$, where $A,B,C$ are constants. Differentiate twice both sides of the approximation above and hence show that $$ \ln(1+x) \approx x-\...
0
votes
1answer
430 views

Steps to Graph Exponential Equations & Absolute Value

how to sketch: $-e^{|-x-1|} + 2$ Can someone clarify: $|f(x)|:$ we draw $f(x)$ and then reflect the ($-y$ parts) in the $x$-axis $f|(x)|:$ we draw $f(x)$ and then reflect the ($-x$ parts) in the $y$...
0
votes
2answers
43 views

Basic Logarithms problems [duplicate]

Can someone tell me how many digits would be there in- $(2.5)^{200}$ and $6^{50}? $ I'm utterly confused where to begin from. Any help would be appreciable.
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1answer
22 views

Characteristics and Mantessa

I've just heard about these terms. Could someone elaborate on what's their use is? And plus could you explain it using a few examples?
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1answer
35 views

Write $b$ in terms of $a$.

If $a$ and $b$ are both positive and unequal, and: $$\log_ab+\log_ba^{2}=3$$ Find $b$ in terms of $a$. Tidying up a bit, letting; $y=\log_ab$ ; and then solving the quadratic gives two solutions. $$\...
3
votes
3answers
51 views

If $a-c = 9$ then find the value of $b-d$.

If $a,b,c,d$ are positive integers such that $\log_a b=\frac{3}{2}$ and $\log_c d=\frac{5}{4}$, if $a-c = 9$ then find the value of $b-d$. We get $b=a^{3/2}$ and $d=c^{5/4}$ Hence $b-d=a^{3/2}-c^{...
4
votes
5answers
128 views

$\lim_{x\to \infty} \ln x=\infty$

I'm reading the following reasoning: Since $\underset{n\to \infty}{\lim}\ln 2^n=\underset{n \to \infty}{\lim}n\cdot(\ln 2)=\infty$ then necessarily $\underset{x\to \infty}{\lim}\ln x =\infty$. ...
0
votes
4answers
44 views

Solve for $x$: $14^{4x} = 3^{-x-3}$ Write the exact answer using base-10 logarithms

I am having trouble with understanding this question and would appreciate some help and guidance. Solve for x. $$14^{4x} = 3^{-x-3}$$ Write the exact answer using base-10 logarithms
0
votes
1answer
33 views

Solution of given equations for $x$ and $y$

Solve for $x$ and $y$ $$(2x)^{\log 2}=(3y)^{\log 3}$$ $$3^{\log x}=2^{\log y}$$ Could someone give some hint to approach this question?