Log Definition and 632 Threads

  1. F

    Solving Log Base Homework: 3 = Log2x 64

    Homework Statement 3 = Log2x 64 Homework Equations N/a The Attempt at a Solution 3 = Log2x 64 2x3 = 64 x3 = 32 x = Cubic root of 32 x = 3.1748 I'm fairly certain the answer has to be 2 b/c 2x would be equal to 4, and 43 = 64. Anyone mind helping me on this one? Probably...
  2. A

    Integrating Logarithmic Functions: Understanding the Integral of Logy

    Homework Statement \int\int-xlogy dy dx the only problem i have is finding the integral of logy i know i have to integrate my parts with u = logy and dv=dy the book says the the integral of logy is ylogy-y but isn't the derivative of logy equal to 1/ylna where a is the base? so isn't...
  3. M

    Solving Log Equations: A Couple of Tricky Questions | Homework Help

    Homework Statement 1.) 3logx2y + 2logxy 2.) 4logabc - 2loga2b - 3logbc Homework Equations The Attempt at a Solution I know that 3logx2 is the same as 6logx but I don't know what to do since there's a y there
  4. M

    Short yet confusing log equation

    Homework Statement Solve the equation log x4 - log x3 = log 3x - log 2x I know the laws of logs and I cleared all the other log questions in seconds but I can't figure this one out Homework Equations I know that log x4 - log x3 is the same as log x4/x3 but what I was wondering is if...
  5. H

    How Does Caffeine Decrease in Your Bloodstream Over Time?

    I'm having trouble with this question. The percent "P", of caffeine remaining in your bloodstream is related to the elapsed time, "t', in hours, by t = 5(log P/ log 0.5) a) How long will it take for the amount of caffeine to drop to 25% of the amount consumed? b) Suppose you drink a cup...
  6. F

    Why do couplings run with log of energy?

    Coupling constants run with the logarithm of energy. This is a result of renormalization, its equations, and the change of the effect of the virtual particle cloud with energy. Is there a simple way to understand why this happens with the log of energy, instead of with another function...
  7. 1

    Derivatives of Log: Find f'(x) for f(x) = log10(x/x-1)

    Homework Statement Question is f(x) = log10(x/x-1), find f `(x) Homework Equations so I used the formula d/dx loga(u) = 1/uLNa . (d/dx U) The Attempt at a Solution (1/(x/x-1)*ln10)*1/(x-1)^2 I used quotent rule for d/dx U part. editing Final Answer I got is...
  8. N

    Solve for x: Logarithmic Equation with Multiple Terms - Step by Step Guide

    Homework Statement log x2 + log x - log 2.7 = log 10 solve for x Homework Equations The Attempt at a Solution this one i really don't know how to do. I can't find any examples, but this is what i tried (youre going to be like, what? but i had to attempt it.) I think when logs...
  9. N

    Partial Derivatives of natural log

    Hey all. I'm having some problems with the partial derivatives of e. I understand the basics such as exy2. where I'm getting confused is with the following dz/dx=e(x+y) and dz/dx=1/ex+ey Can anyone help me out with understanding these??
  10. T

    Fourier Transform of Logarithmic Functions

    Homework Statement Find the Fourier transforms of the following distributions: log|x|, d/dx log|x|. The Attempt at a Solution I'm starting with the second distribution: \langle F(pf(\frac{1}{x})),\phi \rangle = \langle pf(\frac{1}{x}),F(\phi) \rangle where F() is the Fourier transform...
  11. I

    How to Solve Log Equations with a Variable Base

    Homework Statement Log [with base x]216 =6 Find x Homework Equations The Attempt at a Solution Ok, so I put the log equation into exponential form. It now becomes: x^6=216 I'm lost on what to do next.. I've tried taking the e and ln of both sides, but when I check it, it's...
  12. M

    Natural Log of Units: What Happens to the Units?

    Homework Statement We're doing a lab and we basically had to find ln(Pv), where Pv is vapor pressure of isopropanol. Well, the pressure is initially measured in kPa, but what happens to the units if you take a natural log of that whole thing? For example, if I take ln(5 kPa), do the units...
  13. E

    Solving Logarithmic Equations for Homework Help

    Is log49/4+log9/35-log21/10 = log2/3 ? I've tried and I'm here 2log1/5+2log2/5-log7=log2/4 , if I didn't do anything wrong, but I don't know what to do then , please help me !
  14. A

    Average Data from Multiple Excel Log Files

    I have a lot of Excel spreadsheets which are actually log files from a test (so they all have the same structure) and I need to get the data (a number) from a specific cell (same cell) in each file and do their average. Does anybody know an efficient method to do this?
  15. G

    Log Length in L-shaped River Channel

    Homework Statement Two rivers of unequal width (64m and 125m) meet at a right angle, forming an L-shaped channel. What is the longest possible log you can float on it? Homework Equations The Attempt at a Solution I tried for equal widths and built a recursive algorithm for turning...
  16. F

    Using L'Hospital's rule with roots and log functions

    Can someone help me use L'HOP to determine lim x -> 0 [ \sqrt{x}*ln(x) ] ? I'm confused!
  17. J

    Why are log graphs of different equations not all regular parabolas?

    Can someone explain to me why the graph of: logy=logx² is the graph of a regular parabola logy=2logx is the graph of half a parabola (x>0) logxy=2 is the graph of half a parabola except x>0 and x cannot be equal to 1 I just don't understand why they're not all normal parabolas, and...
  18. J

    Integrating Natural Log Function using Integration by Parts Method

    Integrating Natural Log Function using "Integration by Parts" Method Homework Statement The problem says to integrate ln(2x+1)dx Homework Equations I used u=ln(2x+1); du = 2dx/(2x+1); dv=dx; v=x The Attempt at a Solution So, I integrated it using that (above) 'dictionary' and I...
  19. B

    Verify: Is a^(log n) = n^(log a)?

    Hello: I seem to recall a vague truth that a^(log n) = n ^ (log a)? Can someone verify? Thanks.
  20. L

    Can I Plot Log (x) with Error Bars without Changing err_x Values?

    Hello, I have a column of 'x' values, each with an error 'err_x' serving as error bars. My question is: If I need to plot 'log(x)', Do I need to make any changes to 'err_x' to reflect the log operation before plotting them as error bars ? Thank you in advance Lorna
  21. G

    A natural log inequality with absolute value

    Homework Statement F(x) = (8-12ln|x|)/(x^4) > 0 (a) For what values of x is the expression F(x) defined? Write your answer in interval notation. (b) At what value(s) of x is the expression F(x) equal to zero? If there is more than one answer separate them by commas. (c) The set of...
  22. H

    How do I find the inverse of a log function?

    Homework Statement f(x) = log2 x + 3 2 log2 x − 1 how do i find the inverse of this? how do i find the range and domain of a log function? Homework Equationsf(x) = log2 x + 3 2 log2 x − 1 is equal to f(x) = log2 x + 3 - log2 (x − 1)2 D of f(x) = R of f-1(x) The...
  23. J

    Calculate Base 10 Logs Without Calculator

    Is there a way to calculate multi digit base 10 logs without a calc or tables? eg.. what is ? log (base 10) of 1381.42?? (without a calulator)??
  24. R

    Calculating Normal Force of Log on Bullfrog

    A second 0.63 bullfrog is on a log tilted 33 above horizontal. How large is the normal force of the log on this bullfrog?
  25. D

    Integration by parts help natural log hurry tired

    Integrate the function. (3x)/(3x-2) I am spose to use integration by parts but i don't know how to integrate 1/(3x-2). anybody help??
  26. T

    Re-Defining Log: Can We Make it Intuitive?

    Would it be okay to redefine the complex definition of Log and define it for example C\[0,infinity)? I guess then you would have Log z = log |z| + i Arg(z) where -Pi<=Arg(z)<Pi Everything would work fine? But then you can't have Log 5 for example which would be very counter unintuitive.
  27. X

    Evaluating Integral with a natural log

    I hit the submit instead of the preview. please wait Homework Statement \int9s9^s dsHomework Equations ∫udv=uv-∫9^sds-∫vduThe Attempt at a Solution u=9s du=9ds dv=9^s ds v=∫9^sds =∫3^(2s) ds =3^(2s)/[2ln(3)] this is as far as i have gotten. Am i correct so far?
  28. C

    Simplifying Logarithmic Ratios: How Do You Do It?

    how the heck do you simplify this ? (Ln (2x/y) / Ln (x/y)) = m/n HELP ME!
  29. F

    Log laws (possible error in answers)

    ive got integral[(2/(2-z))+(2/(1+2z))]dz=integral dv/v then the next line is ln|v|=-2ln|2-z|+ln|1+2z|+c when i equate this i get rid of the 2 as a common factor integrate the V side first and multiply through by 1/2 giving me ln|2-z|+ln|1+2z|=1/2ln|v| which i don't think is the same as...
  30. M

    Help with log integration/differntiation

    I'm having trouble on these two problems. Can anyone give me a step by step explanation on how to do them (or one of them)? 7. Find f'(x), if f(x) = \left|\frac {x^2\left((3x + 2)^{\frac {1}{3}}\right)}{(2x - 3)^3}\right| 13. Perform the integration: (a) \int(x-1)e^{-x^2+2x}dx (b)...
  31. J

    What is the graph of y = log base 1 x?

    I know that logarithms to the base 1 is undefined, due to the reason that: \log_1{x} = \frac{\log_a{x}}{\log_a{1}} And this leads to divison by zero, which is undefined. There was a question in one of my textbooks that asked describe the graph that results if y = \log_1{x}. Is such a graph...
  32. I

    Understanding Natural Logs and e: Simplifying Expressions with ln and e

    I am starting my first year of college and I reviewing my high school notes from trig pre-cal and there was one thing I couldn't figure out. It was a multiple choice question and I don't have the textbook anymore but the answer I circled I can't understand how I arrived to that answer...
  33. A

    Solving Natural Log Equations: Tips & Tricks

    Homework Statement sqrt(ln(x)) = ln(sqrt(x)) Homework Equations The Attempt at a Solution I've been trying to do this for some time now. Could anyone give some tips on how to get started with this?
  34. X

    Is My Derivative Calculation for a Logarithmic Function Correct?

    1. Given Y = ln [ (x+1)^3/((x^2)-1)^(1/2), find y' 2. I came out with the following answer to this question: (3x-4)/((x^2)-1) How ever, I typed the question into an online derivative calculator (to hopefully check my asnwer as I have no answer key, and want to make sure I'm on the...
  35. X

    Derivative of a Log function: Y=ln( )

    1. Given Y = ln [ (x+1)^3/((x^2)-1)^(1/2), find y' 2. I came out with the following answer to this question: (3x-4)/((x^2)-1) How ever, I typed the question into an online derivative calculator (to hopefully check my asnwer as I have no answer key, and want to make sure I'm on the...
  36. humanino

    Google/Youtube log, 14 terabytes to Viacom

    I am glad I never created an account on youtube. I do not use it much. Viacom will not be able to know which video I have been watching. I wonder, once they found you watch copyrighted material every day, what will they do about it ?
  37. T

    How Do You Solve log_{2}8x^{2} When log_{2}x Equals p?

    Homework Statement Given that log_{2}x = p a) Find log_{2}8x^{2} in terms of p The Attempt at a Solution take the power outside the log 2log_{2}8x but i can't see what to do next Any suggestions Thanks :)
  38. T

    Understanding Exponential and Natural Log Rules: Is this Simplification Correct?

    Is it true that e^{2(2x+ln2)} = e^{4x}e^{2ln2} I can't see how that is true? According to a paper mark scheme it is. Can someone clarify Thanks :)
  39. T

    The coefficients of a power series for natural log

    Homework Statement The function f(x) =ln(10 - x) is represented as a power series in the form f(x) = (sum from 0 to infinity) of c_{n}x^{n} Find the first few coefficients in the power series. The Attempt at a Solution I know how to find the coefficients in a normal looking...
  40. D

    How do logs work with multiple bases and negative exponents?

    how do logs work when it's like this. 3 log10 y = -2 log10 y = a 10^a = y so it's 10^-2 = y but where does the 3 go, and why does it go there. I'm not sure.
  41. F

    Finding a limit with the natural log function

    i need help with this: lim x->\infty of \frac{ln(2+h) - ln(2)}{h} i have no idea where to even begin! i tried resolving it, but it didn't help :[ any suggestions??
  42. D

    Question of enthelpy of vaporization the diference from ln to log

    hi, I'm new around here but i really need your help this question is similar to one already solved here some years ago so my problem is: 1.The vapour pressure of benzene between 10°C and 30°C fits the expression log(p/Torr) = 7.960 - 1780/(T/K). Calculate (a) the enthalpy of...
  43. R

    Solving Strange Log Identity - Richard

    Hey folks, I'm reading the paper: http://arxiv.org/abs/hep-ph/0301168 and I'm trying to make sense of the first line of eqtn 44 where he states that we can write: \frac{1}{2}\sum \int\frac{d^{2n}k}{(2\pi)^{2n}}log(k^2+\frac{m^2}{L^2}) as...
  44. B

    Mathematica Plot X-axis Log & Y-Axis Linear with Mathematica LogPlot

    I am a new user of Mathematica software, and need to plot a quite complicate function using a semi-Log type plot. The function that the software provides is LogPlot however this function plots the Y axis in Log scale and the X in linear scale, but I need the exact opposite, to plot the X axis in...
  45. E

    Uncovering the Mysteries of Log Laws: Exploring the Equations e^lnx and 8^log8x

    I don't know how I managed to forget this one, but I did somehow... If there's something like: e^lnx, why is that equal to just x? and same goes for sokmething like: 8^log8x which is just equal to x. I'm just wondering how, algebraically, one could show this to be true.
  46. A

    Distribution of Log of Random Variable

    Let X and Y be random variables. X ~ N(u,s^2) Y = r ln X, where r is a constant. What is the distribution of Y? (This is not a homework problem. It's just related to something I was curious about, and I can't figure out how to solve this, if it is solvable...)
  47. T

    Solving Unusual Log Problem: Find x in ln(x+2)-ln(x+3)+ln(x)=1

    Homework Statement Solve for "x" in the equation: ln(x+2)-ln(x+3)+ln(x)=1 The Attempt at a Solution This unusual ln problem really has me stumped with what to do and usually this stuff has given me no problems. I can't isolate the x because e is always in the way of solving it...
  48. P

    Simplify fully: log a + log b – log b^2

    Homework Statement Simplify fully: log a + log b – log b^2 The Attempt at a Solution I don't even know where to start...
  49. A

    How to solve a Nonhomogeneous differential equation with natural log?

    y''-y'-30y=ln(t) My attempt: i tried to use the method of undetermined coefficients. y''-y'-30y=ln(t) Y(t)=A lnt Y'(t)=A/t Y''(t)= -A/t^2 I also tried: Y(t) = A ln(t) + B 1/t + C 1/t^2 now I am stuck...any help??
  50. G

    Different ways that Log appears

    Not so much a question query here but a query about how my question is written. Im having to do some integration and my question has one part loge (log sub e). I think that this is just natural log which i usually see written as ln(x). Is this correct? However my table of integrals has...
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