Reflection in y-axis

[sysD]

sorry, dumb question.

Edited March 24, 2011 by sysD

[Xittenn]

Check both possibilities using a graphing calculator, this will immediately enlighten you to the difference between each of [math] f(-x) [/math] and [math] - f(x) [/math]

[sysD]

------

 

okay, so that was something i could have figured out if i wasn't dead tired =p

i've got it now.

 

but here's something.

 

y=-2log_3(x-3)-1

 

I've graphed this out and there seems to be an asymptote at x=3. Intuitively, I can say that x cannot be less than 3.

HOWEVER.

 

When I graph with a calculator, it shows values at x=2 and below.

How can this be? (eg coordinates= (2, -1), (0, -3)

Edited March 24, 2011 by sysD

[Xittenn]

I'm sorry is that [math] y = -2 \log_3 (x-3)^{-1} [/math]? I need to see it properly regardless to think right, I have a hard time with symbolic representation.

[sysD]

y = -2log(base3)(x-3) -1

 

here's the wolfram page.

http://www.wolframalpha.com/input/?i=%283%29%28log%289x-36%29%29%2Flog%283%29%29-13+

 

the negative one is the vertical shift of one downwards, not an exponent (incidentally, how do you type like that?)

Edited March 24, 2011 by sysD

[Cap'n Refsmmat]

Here's the tutorial on the fancy mathematics:

 

http://www.scienceforums.net/topic/3751-quick-latex-tutorial/

 

You can click on any equation you see to learn how it was done. There's a popup with the appropriate code.

[Xittenn]

Your wolfram post confuses me

 

This is what you have posted here. What you have posted there has an asymptote of 4 on x because 36/9 .... and this is a bit of a jump from your op :/

[sysD]

oh, im sorry. i was working on another problem and i must have mixed up the two pages. the wolfram page you posted is the correct one...

 

and yeah, haha, i know it is a bit of a jump. but i realized the answer to my op and instead of creating a new thread for another question, i just decided to put it here instead.

 

[math] y = -2log_3(x-3) -1 [/math]

 

(thanks, cap'n)

 

so how can x be less than three? in other words, i know the vertical asymptote isn't crossed, but how can there be a log(-1)?

Edited March 24, 2011 by sysD

[Xittenn]

Ok I thought you had written [math] y = -2 \log_3 (x-3)^{-1} [/math] your new one is [math] y = -2log_3(x-3) -1 [/math] and that corresponds to this which makes more sense ...

[sysD]

sorry bout that, now that i know how to use latex it'll be easier to express equations from now on

 

any ideas on how to get values from log(-1)?

that seems to me to be an invalid domain. yet wolfram yields results

[Xittenn]

Reread the definition for asymptote ... . . . . . .. .. . . . .. . .

[sysD]

an asymptote is a value that cannot exist and other values approach that limit, right?

 

sure, i get that, but lets forget about the asymptote itself.

 

how can this:

 

[math] y=log(-x) [/math]

 

be valid?

[Xittenn]

Sorry shouldn't use wolfram alpha use Maxima.

 

 

Should look like this ^

[sysD]

thatt seems proper.

 

why would wolfram show me that though? is it the exponential equivalent of imaginary numbers?

[Xittenn]

It was graphing the complex values, yes . ... . . . .

[sysD]

can you link me a guide on that? i'm not really sure where to start.

something pertinant to the example would be helpful

[Xittenn]

Blitzer

[sysD]

If I could afford a 200$ textbook I'd just get tutoring and wouldn't be here. Thanks for everything.

[Xittenn]

$20 used :|

 

College Algebra is also something you will find in, at the very least, the downtown public library. You learn so much more from books and the internet just hacks your brain to little pieces.

 

It's really just what I've always done, before I started buying books I got them from the library, sorry if I offended you.

[sysD]

yeah, sorry if i snapped.. it was like 6am and I'd been up all night typing out equations. I'll hit up the library, thanks

[Fuzzwood]

Stops nicely at x=3 on my graphical calculator. Of course, I do know the trick of alogb = 10logb/10loga to convert logs with different bases into eachother.