 # Ragib

Senior Members

193

## Everything posted by Ragib

1. How about $\int^1_0 \frac{\ln (1+x)}{x} dx$ .
2. $\int \frac{1}{x\sqrt{x}\sqrt{x-1}} dx$ Let $x=\cosh^2 u$, then $dx = 2 \cosh u \sinh u du$. $\int \frac{2\cosh u \sinh u}{\cosh^3 u \sinh u} du$ = 2 \int \sech^2 u du $= 2\tanh u + C$ $= 2\tanh (\cosh^{-1} \sqrt{x} ) + C$ EDIT: LaTeX was not working for those two lines, so I ommitted the tags so people could see what I meant to type, and hopefully someone can correct my 'LaTeX syntax error'. (Fixed the LaTeX for you. It turns out there's no \arccosh command in LaTeX, so I had to make do with cosh-1. Oh well. -- Cap'n)
3. ## Powerful calculator needed

Very simple and fast program that works up to 5011 digits. Extremely useful. Bcalc.zip
4. But possible with a slightly more powerful geometry of origami
5. Umm well first, its df/dx, and its as h -> 0. I have no idea what your method is trying to show, but that only works for polynomials anyway. The OP wants a general one for all functions.
6. Well it says it has to be proven for all positive values, and I can't say the answers have to be the same, so I would assume they can be separate values.
7. Let $x=u^2$, and do as Bignose said. The integral becomes $2\int \frac{u^3}{1+u} du$, which with some easy polynomial division will get you $\frac{u^3}{1+u}=u^2-u+1 -\frac{1}{1+u}$. Split the integral in two, you get: $2(\int u^2 -u +1 du -\int \frac{1}{1+u} du$. The first one is easy, reverse power rule. The second, do some substitution. So you should get $2(\frac{u^3}{3} - \frac{u^2}{2} + u -\log_e |u+1|)$. Substitute $u=\sqrt {x}$ back in EDIT: Btw I checked the answers, its correct
8. I dont want to think of it this way, but deep down I think the gloryious days of science are gone, when the recluse in his shed, or the small time amatuer can make a decent contribution. In mathematics its still possible, with some genius, but these days with physics you need at least 3 now.
9. My bad, I guess I have seen that equation before then Sorry, My Brains Been farting alot recently..
10. Unless your saying $\frac{a}{2} dt$ is equal to zero, that equation is incorrect. In other words, velocity is equal to zero. Otherwise Its wrong. I've never seen that equation before.
11. Well, heres my best shot. Ok, well the rule applies to composite functions, say f(x)/g(x). When we sub in values we get an indeterminate form. We only want the RATIO of the 2 functions. So say 5x/x, x appraoches zero, 0/0. But since we only want the ratio, we could instead get an approximation that, in the limit, is exact. Our approximation is our tangent line The tangent line has the same value as the point it touches. So basically we found the ratio of the values at the tangents, which is what L'hopitals rule wants. I hope I explained that well...
12. Well since there is both sin and cos in one equation, all i can think of is t substitution. Let t=tan(x/2), since you know the the expansion for tan(x+y), let x=x/2 and y=x/2, that way tan x= 2t/(1-t^2). Right a right triangle, set 2t the opposite side, 1-t^2 the adjacent, use pythagoras for the remaining sides. Then the opp/hypotenuse ratio is sin x, and do the same for cos. Make the substuitions for cos and sin into the last equation, solve for t and you can get a quadratic equation, which is easy to solve. Good luck
13. Anyone? Come on, at least the 2nd problem...
14. I don't think that is correct sinisterwolf, can you give me your values for x y and z seperately? That doesn't look right..
15. O yes I knew you were in Canada, I just assumed you logged the forums in the afternoon, and 9 hours after that would be pretty late. 1am is quite late, though since its holidays I regularly go to sleep at 3am and wake up at 2pm :S. So to the question, someone try to do it please. Possibly Induction? To tell you the truth guys I havent done it either, but I remember the proof was relatively simple. Heres another short problem, that requires very little knowledge, pretty much just basic algebra. What is the square root of i? Background info for newbies: i is the square root of -1. All complex numbers can be written as a+bi, where a is the real, normal everyday number, and bi and a real everyday number times i. Simple from there.
16. O sorry, forgot the +C on the first integral.
17. Q1. $\int x^3 dx=\frac {x^4}{4} \therefore \int_0^b x^3 dx = \frac {b^4}{4}$ Q2. a- doesnt make sense, b makes no sense either. Q3. I cant be stuffed doing it manually, 15.0323801 approx.
18. Lol Seeing as your other posts was 9 hours ago, and thinking it was in the afternoon, maybe you should lol.
19. I can't be bothered to, could you expand 2cos(x/2 + pi/4)sin(3x/2 - pi/4), take the terms to one side and make any simplifications you can. Then I'll help you find the other solutions.
20. Yes, that is correct. Anyone want to attempt an algebraic proof?
21. Lets say m=0, then the Series is equal to 1. m=1, the series is 1 + 10, 11. m=2, 111. Find the pattern in the squares.
22. 1. 2.97 Celsius 2. The electrons, primarily the outer shell. 3. Atomic Number is the number of protons, atomic mass is protons+neutrons, so the difference is the number of neutrons. The number of protons are the same as the number of electrons. 4. Heating the atoms up and seeing what wavelengths are emitted. 5. Main Group? Thinking you mean Transition metals, it varies. 6. Diatomic Elements are elements that are found as molecules of 2. Most gases, ie Oxygen, Nitrogen etc, You find 7 gases... 7. Ionic Compounds are formed by exchanging electrons to achieve an overall neutral charge. Covalent Bonds are when the atoms share pairs of electrons, to give each other the illusion of a full outer shell. Covalent Bonds are usually stronger. 8. You can not change the total number of original atoms, total atoms of each element. You can change the number of each element in one of the compounds, as long as you balance it to satisfy what I said before. Hope this helps, Good Luck.
23. Ok Guys, you have to admit, these forums are pretty quiet for some reason. Im going to post a problem for someone to figure, ill start off relatively easy: $(\sum_{n=0}^{m} 10^n)^2$ Gives what general Form? Its ok if you can spot the pattern, but try to prove it as well.
24. Omfg, Fun with ALGEBRA? For a formal proof you need 3 dimensional calculus...at least the proof i can think ok...
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