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#2 Re: Help Me ! » combining algebra fractions » 2013-07-15 19:47:55

sorry to bug in, but here is were the logic you have fails, and the book is right
instead of having a-d and a+d, make the a-d=m and a+d=n
what you got:
d/m+a/n=(dn-am)/mn
ok, plug in the stuff
(d(a-d)-a(a+d))/((a+d)(a-d))
big excalmation point, sighn warnings
now if you split them the top part
da-dd-aa-ad=-dd-aa
bottom
(aa+ad-ad+dd)=aa-dd
simplification is only posible is some cases!!!
the a is a variable(wich i am assuming) so is b
if you go with a =7 and d = 1
thy them out
what do you have
7/(1+7)-1/(1-7)=7/8+1/6=25/24

to the formula you have got you get a minus(aa+dd) wich is allways negative or 0 and the solution is positive

#3 Re: Help Me ! » limits of a sum » 2013-07-15 19:21:31

ok, after some digging i have found a somewhat close problem, but i still do not understand how did they come up with the answer:
lim of n tends to infinity of sum from k =1 to n of 1/k(k+1)
this is the problem, and the solution given by the book is
you take out the sum and
sum of k=1 to infinity of 1/k -1/(k+1)
wich i get, you just split the terms since you have multiplication not summation
then that equals to 1-1/(n+1)
how do you get that summ?!?!
and the last step lim of a constant = constant and lim of 1/(n+1)=0 witch i get

#4 Re: Help Me ! » limits of a sum » 2013-07-13 06:44:39

you are absolutely right,
i got nothing but a bunch of sin and x^4th power, and i do beleve what i am doing is wrong,
but still , i will try and solv this integral, who knows maby i will get lucky and do it , and i hope it is equal to something interesting big_smile
new stuff to learn
later edit:
ow god please do not tell me it is equal to pi/2

#5 Re: Help Me ! » limits of a sum » 2013-07-13 06:00:40

ok, read the pdf and you are right good sir, half of it is gibberish, getting real numbers and stuff, and not even pretty ones, how come?
anyways, here is hoping
bobbym, i really appreciate you spending some time trying at least to point me in the right direction,
for me is just like a bloodhound finding meat , 1 morsel at a time, and you just said:" here boy here, the big stake is inside the pen, "
I just go wof and find the way to get in

#6 Re: Help Me ! » limits of a sum » 2013-07-13 05:38:27

my apologies for bad English, basically you are asking me if i kno how much is lim when x tends to infinity of 3x^3/(x^3+etc), just some simple math 3/1=3(no problem we got this
1^ infinit power=(we got this ) a function tends to 0 we get 1+that function to the power of 1 over that functon[wich is e] and that function again to the power, and if any other power remains(usually dose) you just to the reamining limit
(if someone is reading this and i just spoiled your joy of finding a solution to some problem,sorry)
do not ask me , maby he felt sadistic or thought we cannot do it
we found the easy way to solve for m in the following eq( a*sin(x)+b*cos(x)=m[probem was so find the min and max values for m given a and b(our pik, and the easy solution my colleague found is to just use tg(x/2)=t and the rest is math)]) so we are not that uncooperative, but if we have no idea were to look, anyway, thanq for at least trying to give me some direction on the solution will keep update if found solution solo or whatnot,

later edit, hold the phone, that pdf looks promising, leme just read it, may take a while

#7 Re: Help Me ! » limits of a sum » 2013-07-13 04:45:13

finished 11 grade, but my teacher never bothers to tech in order, we have done some integrals so we can do some problems for the BAC (our final exams in 12th grade) indefinite, definite, ... , matrices , as long as you do NOT use a calculator any method of pen and paper is good method of pen and paper,
later edit: as long as you provide the formula you use and i get the same result for just 1 example, i should get something for other 6 as well, just ask if i kno and i will try to answer to my best of my ability what i understand from what you stated
(I am seriously freaking out here since you got the results so fast and actually might now the generic formulas witch i could apply)

#8 Re: Help Me ! » limits of a sum » 2013-07-13 04:15:43

they are problems for the summer vacation, for us the nerds, omg, me a nerd, now i have done it, anyways it is just 3 pieces of paper with problems on them, but since i have no idea on how to solve these specific problems, and neither do my colleagues kno were to start at least, I had the idea to ask, found easy ways to solve some of the problems in this sheets, but for these ones, not as much as a hint, (re-looking Euler Mclaurin summation atm,) stil not convinced that this is the way, but since you got some results, might just be worth checking, also finding and just typing results on the paper is of no use, if we get this on a test next year, who will explain this again, we need to understand what we are doing if we are to help others so we get passing grades, and you got 0 and 1 sses, all we got were quote"say infinity, n tends to infinity so infinity", sorry for long post and boring math trolling, but seriously what or how did you get those answers,
later edit:you have a talent or someone showed this type of problems before and now you are just teaching it, anyways, many thx for the reply, congratulations on finding anything different from infinite and if you  have the patience please share the method you used

#9 Re: Help Me ! » limits of a sum » 2013-07-13 03:37:15

I am not going to argue since i've got no idea on what or how you managed to get any answer, congratulations, but how did you do it?

#10 Re: Help Me ! » limits of a sum » 2013-07-13 01:53:53

it just means that there are 7 problems and that they are all exacly the same exept for the k* part
a is just k
b is k^2
c is sqrt(k)
d is sqrt(k^2+1)
e is sqrt(k^2-1)
f is (k+1)(k+2)..(k+n)
g is (k)!*n!

so if you would ask what c is at the example :
lim when n tends to infinity of (sum from k=1 to n for(1/(n+sqrt(k))

#11 Introductions » hello evreybody » 2013-07-13 00:55:43

rete
Replies: 1

nice to meet you all and nice to see pepole still carrying on the good ol fight of finding the ex big_smile
i am from romania and i try and solve for x

#12 Help Me ! » limits of a sum » 2013-07-13 00:52:19

rete
Replies: 21

Hello everybody i  have a couple  of problems
most of them sound like this : lim when n tends to infinity ,( for sum of k=1 to n for [1/(n+k*)])

this k* is important bcoz it keeps changing form, is either, k^2, or sqrt(of k), or sqrt(k-1), or k, etc ...
but the basic problem is how to do it in normal mode

it must be a way to solve this problem but i just have no idea were to start,
if you see a solution, and have it in any detail, it would be much appreciated

also if you have some idea on the following:

f(x)= e^x+nx+3
solve for f(0)(wich i can, easy , just plug in 0 for x and get the answer)
f^(-1) of (3)=
basically sates in the book find f(3) and f^(-1) (3)
i will try and type in latex
any suggestion, comment, idea on any of these would me much apreciated

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