/sci/ - Science & Math

[Anonymous No.3322674]

ok /sci/entists there's this function:

f(x)=lgx+2x^2

I have to find the inflection point.

so I find the derivative y'=1/x + 4x

the problem is that 1/x +4x -> (4x^2+1)/x
then 4x^2=-1 that's imaginary.

but according to WA i'm missing something.

Function: http://www.wolframalpha.com/input/?i=logx%2B2x^2

Derivative: http://www.wolframalpha.com/input/?i=4x%2B1%2Fx

WTF IS GOING ON?

[Anonymous No.3322719]

BUMP

[Anonymous No.3322840]

[Anonymous No.3322950]

>the problem is that 1/x +4x -> (4x^2+1)/x
then 4x^2=-1 that's imaginary.

It should be 4x^2/x =-1/x

It even makes sense. What rate of change from a function that isnt imaginary, is going to even have a rate of change.

I dont really get what you are looking for here for an answer. Are you trying to find critical points or integrate?

[Anonymous No.3322962]

>lg

fuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu

[Anonymous No.3322985]

>>3322674

<span class="math"> \displaystyle{ f(x) = \log x + 2x^2 } [/spoiler]

<span class="math"> \displaystyle{ f \prime (x) = \frac{1}{x} + 4x } [/spoiler]

<span class="math"> \displaystyle{ f \prime \prime (x) = 4 - \frac{1}{x^2} } [/spoiler]

<span class="math"> \displaystyle{ 0 = 4 - \frac{1}{x^2} } [/spoiler]


<span class="math"> \displaystyle{ 4 = \frac{1}{x^2} } [/spoiler]

<span class="math"> \displaystyle{ x = \frac{1}{2} } [/spoiler]

[Anonymous No.3322991]

>>3322985
Well, that's the last time I use \prime... Those things are ugly as fuck.

[Anonymous No.3323011]

>>3322991
Just curious, how do you do new lines in LaTeX on here? the \\ doesn't work, do you just use new math tags for every line?

[Anonymous No.3323021]

>>3323011
Yeah, it's kind of annoying.

[Josef !!nUf2NflSAyw No.3323056]

>>3322991 prime ugly
That's because you're not using them correctly. When you're typing a normal ', it's automatically converted to a superscript prime. A Latex \prime has the size of a normal letter, ready to be super-sub-whateverscripted.
': <span class="math">f'(x)~f''(x)[/spoiler]
\prime: <span class="math">f\prime(x)~f\prime\prime(x)[/spoiler]
^\prime: <span class="math">f^\prime(x)~f^{\prime\prime}(x)[/spoiler]

[Josef !!nUf2NflSAyw No.3323066]

>>3323011
>the \\ doesn't work
It's disabled for no good reason I could possibly think of.
>do you just use new math tags for every line?
That's the only way I'm aware of, yes.

[Anonymous No.3323076]

>>3323056
I see... Thank you, sir Josef.

[Anonymous No.3323111]

>>3323066
Probably cause it'd induce spam
or not

[Anonymous No.3323228]

>>3323111
hasn't stopped people before. There are other commands to make you scroll a whole page length, or 10.

[Anonymous No.3323235]

>>3322985

thanks

>>3322950

yes, I need to find the inflection point if there's one.

[Anonymous No.3323249]

>>3323235

dumbshit find the second derivative and find when it equals 0.

[Anonymous No.3323285]

>>3323235

ok I found them.

x=±1/2 y=0.1931

[Anonymous No.3323298]

>>3323285
What the fuck! x=-1/2 is not inflection point, the function isn't defined there.

[Anonymous No.3323306]

>>3323249

yeah I love you too.

[Anonymous No.3323314]

>>3323298

oh really?

http://www.wolframalpha.com/input/?i=logx%2B2x^2