lizzy16 Posted March 10, 2011 Report Posted March 10, 2011 Does anyone here understand logs, ln and all that stuff? I'm a bit lost..and while I have no specific questions those who are confident in this could perhaps let me know so over the next week I could ask for help if I need claryfying? I'm lost and I don't have the time to stay after and none of my peers really understand it either. Quote
Dravin Posted March 10, 2011 Report Posted March 10, 2011 (edited) I know about logs and the like, I've not specifically dealt with them in relation to trigonometry though. But if you have questions I'll do my best. There are math gurus on the board who can probably help too (I don't consider myself a math guru).I suppose the first question you should probably ask is about the first "Huh?" moment you had that didn't get resolved in class. At least until you can come up with something specific.Edit: In relation to your title.Log without any subscript is base 10 (called the common log). LogX=Y can be thought of as 10^Y=X. So it takes a number (the X) and tells you what you have to raise the base by (in the common log that would be 10) to get Y. So Log(100)=2 because 10^2 = 100. ln is the natural log and is the same idea but the base is Euler's number (e) instead of 10. So ln(e^2)=2. Put like that' it's obvious (that to get e^2 you raised e by 2) but e is an irrational number so I can't accurately imput it without using e, but ln(7.3)=~2 because 2.7^2 = ~7.3. (Obviously e is being approximated by 2.7 kinda like how you write pi as 3.14). Note: X > 0 , there is nothing you can raise e or 10 to that returns 0 or a negative (remember X^0 = 1 and X^-Y returns 1/X^Y which can be a very small fraction but is still greater than zero). So that is the difference between ln and log, it's the same deal just a different base. You may also encounter in your classes log2X=Y which can be* 'pronounced' log base 2 of X equals Y. Also 1 as a base doesn't work as 1 raised to any power is 1, and if you did have log base 1 of 1 equals Y, well Y could be any real number (try solving by intuition 1^y=1 to see what I'm getting at). Other than that though any positive number will work as a base, though e, 10 and 2 are the most common. * That's how I was taught.Now e^-1 is the same as 1/e, just like how 2^-1 is 1/2. The fact that it's e may be throwing you off, but it's just a number, think of it as a weird way of writing 2.7 if that helps.Quick Quiz (sorry to be patronizing if I am) but what is Log1000 equal? ln(1/e)? Log base 0.4235 of 0.4235^235? Edited March 10, 2011 by Dravin Quote
rameumptom Posted March 10, 2011 Report Posted March 10, 2011 Sorry, no math skills like that here. However, if you need help in history, literature, archaeology, natural science, biology, cosmology, cosmetology (jk), etc., I am here for you. Quote
pam Posted March 10, 2011 Report Posted March 10, 2011 Do we need to start a forum for math education? Quote
Wingnut Posted March 10, 2011 Report Posted March 10, 2011 Do we need to start a forum for math education?MOE could be the moderator. Quote
slamjet Posted March 10, 2011 Report Posted March 10, 2011 The way it looked, I thought I would set off some nuclear device by clicking on the topic. Quote
Dravin Posted March 10, 2011 Report Posted March 10, 2011 The way it looked, I thought I would set off some nuclear device by clicking on the topic.And yet you clicked anyway?/me calls Homeland Security. Quote
slamjet Posted March 10, 2011 Report Posted March 10, 2011 Yea, well my ex can use the life insurance money. Quote
lizzy16 Posted March 17, 2011 Author Report Posted March 17, 2011 expand: log xy/z how? and why? Quote
MrShorty Posted March 17, 2011 Report Posted March 17, 2011 If I understand the meaning of "expand" you should have a proof somewhere that the log of a product equals the sum of the log's of the factors. log(a*b)=log(a)+log(b). Does that fit in with the section you're studying? Quote
Guest Posted March 17, 2011 Report Posted March 17, 2011 (edited) expand: log xy/zhow? and why?Expands to log x + log y - log zWhy?Because of the 1st and 2nd laws of logs.First law: log ab = log a + log b2nd law: log a/b = log a - log bDo you need proof of the laws? Edited March 17, 2011 by anatess Quote
lizzy16 Posted March 17, 2011 Author Report Posted March 17, 2011 i have the awnser sheet. And, thats not it Quote
Guest Posted March 17, 2011 Report Posted March 17, 2011 i have the awnser sheet. And, thats not it Then either your sheet is wrong or I don't understand what they mean by "expand". Quote
mordorbund Posted March 17, 2011 Report Posted March 17, 2011 (edited) l . o . g . . . x . y . / . z Edited March 17, 2011 by mordorbund Quote
slamjet Posted March 17, 2011 Report Posted March 17, 2011 The log of a product is the sum of the logs. The log of a quotient is the difference of the logs. log xy/z log xy - ln z log x + ln y - ln z Quote
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