mathtask :>

by RazZaH • 4 Sep 2008, 13:45 • Journals

ye we did that today at school

tbh its pretty easy if you know some rules :P

f(x) = sin(x) / x³

tell me f'(x) and f''(x)

have fun ::D:DD.D

if u need a hint just tell me..

btw

f'(x) != cos(x) / 3x² ..

some rules you need...but know them just in german

Produktregel: f'(x) = u'(x) * v(x)+u(x)*v'(x)
Quotientrefel: f'(x) = (u'(x)*v(x)-u(x)*v'(x)) / x²

f'(x) = (x*cos(x)-3sin(x)) / x^4

then first rule @ x*cos(x) ->

u' = cos(x)+x -sin(x) -3cos(x)
v' = 4x³

if u fill this in ...

f''(x) =

(cos(x)+x-sin(x)-3cos(x)*x^4-x*cos(x)-3sin(x)*4x³) / x^8

then you can make this one smaller....but i was 2 lazy and just did it a bit smaller lol

f''(x) = (cos(x)+x-sin(x)-3cos(x)*x-x*cos(x)-3sin(x)*4) / x^5

kk prolly ive made a typo or something...but i hope most of u know what i wanted to calculate lol

i hope i could refresh some of ur brains xD

have a nice day :P

easy, what class are you

12

we are learning some "Differenzialregeln" for tehe upcomming staff...

this is pretty easy.....but i want to see if u can solve it ;)

Parent

I can but you prolly cant do it yourself and you need it for homework xD nice trick

anyway mathe sucks!!! mathe gk ftw

Parent

Mathe GK ftl, just like LK and math in general actually.

Parent

U NERDS FUCK OFF WITH SCHOOL !

f'(x) = (x³ * cox (x) - sin (x) * 3x²) / x^6
? :D

noes :P

Parent

wat is wrong in my pattern then? oO

D f/g = (g * Df - f * Dg) / g²

Parent

hint...

sin(x) / x³ = -3 * sin(x)

Parent

but it's different to do derivation in division tasks -_-?

D sin (x) = cos (x) yes
D x³ = 3x² yes

but D sin (x) / x³ = (x³ * cox (x) - sin (x) * 3x²) / x^6
AFAIK o:O

Parent

Definitely.

Parent

wasnt sure here...i didnt write this into my folder...only the next steps

Parent

You're right...

Parent

huh ':) almost thought I screwd :D

Parent

maybe there are other methods to do this :P dnno

Parent

as if you know it yourself... you only want the solution without doing it your self x)

shall i send u the solution per pm?

Parent

no need... [ger] mathe lk - 13 [/ger] izi pWnage

Parent

^^ im math lk 12 :P

Parent

WOOOOOOOOOOOOOOOOOOOOOOOOOOW.

4317

go do your homework without us

>:D

kk ill edit it and hint the solution....

Parent

had an exam about this...but now i dont even want to think about this things
finnished math \:D/

first is easy... but f''(x) something with - sin(x) ... w/e :D

Since I have nothing better to do, answer in a few mins I guess :l

jasper omg jasper

Parent

f'(x) = (cosx) * (x³) - (sinx) * (3x²) / (x³)²
too lazy to continue :S

i failed at math exams...

f(x)=sin(x)
f'(x)=-cos(x)
im not sure :/
boy i need to repeat stuff before school starts next week :[

without the -

Parent

f'(x) sin (x) = cos (x)
f'(x) cos (x) = -sin (x)

Parent

f(x)=sin(x)
f'(x)=cos(x)
f''(x)=-sin(x)
f'''(x)=-cos(x)
f''''(x)=sin(x)

:P

Parent

hard shit

Parent

i want to use the perfo joker

e^x² + 8 / x³ + 1

Parent

And I don't want to do derivatives!

Parent

hard shit

Parent

I could solve it, but I don't want to :(

Parent

hard shit

Parent

does this have something like sinx/x~x somwhere in it? Passed the exam months ago, so i don´t remember anymore. Could be dead wrong

pff, i thought you wanted some razzle dazzle solution instead of brutally using the formula

What point do you want the derivate? The (f/g)' is (fg' - f'g)/g^2. There is probably a more elegant method that gives an equivalent answer but thats not the point here. Is it?

we ve learned this at school today...dont know if there are other methods :P

Parent

Why do you need to look at so much formulas when the derivate is so logic -_-. f'(x) is so wrong calculated :).

Parent

I like how you say it's pretty easy when you know the rules and then show your solution, which is completely wrong. Well done :-)

its not completly wrong :x

then all my books are bullshit and all the rules

look at the solution again -.-

Parent

Just do it with this rule: f'(x) f/g = (g * f' - f * g') / g^2
:) thanks for refreshing my memory about all of this stuff 8)

Parent

isnt it the same rule like i ve used ?

but u can use it only if u devide

not if u multiplicate

then it has to be u'*v+u*v'

Parent

I guess it is :d was so confused after you said my first answer was wrong.. :)

Parent

sry if i confused u lol

Parent

The solution is right, it's just simplified.

That is, for the first derivative, I didn't check the second. Which looks really wrong on first sight, you can't randomly divide away x's :l But I don't know if I'm mistaken or not in this case, it might just be right, my memory may have failed me

Parent

Oh well, in that case it's fine, I just took a quick glance and assumed that (x^3)^2 is x^4 for him ;D I didn't expect him to have a correct solution after he said sonight's is incorrect :c

Parent

Same here, Sonight has the right solution, and I made your mistake at first though and was "wtf'ed" (about the x^3² = x^4) ;D

Parent

u' = cos(x)+x -sin(x) -3cos(x)

That is wrong anyway, unless by x -sin(x) he means -xsin(x).

Parent

I guess he does, else it'd be wrong indeed. :)

Parent

maybe ive written it wrong from the board :P

Parent

u'v - v'u /v²?

panda's journal was diffrent, it was finding a solution which is unique and fun to do so, this is just random math task
oh god razzah oh god, cant believe yo uare 17 :(

after i failed in my computer science studies, i never thought about it again

BRICKS WILL BE SHAT

aaaa boring&nottoohard.
im tring to do
Prove, that for optional integers image: 4ec965b1c6be1c731abc50776a0319ee

Inequality is granted image: 520f3dc04935ec8bcf2a2393544f6901

my stiupid math teacher wants me to do 6 of 12 tasks of polish matholimpic :( coz i wasnt on last 3 lessons :(
heeelp!

Optional integers?

Parent

dowolne liczby calkowite kociaku

Parent

care?

thanks for reading my mind

Parent

Np honey, np.

Parent

my brain is going to implode if i think longer about that shit lol^^

Errrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr?????????

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