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mattmns

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Do you need to understand the problem? What is your dad's background?

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DaveC426913

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GCT

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how do you know your dad's answer is accurate, not necessarily bogus, but he might be off the mark

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heman

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Shippo said:

Well there is a question in Mathematics which My teacher asked me when i was in 11th class and i haven't come across anybody who could suggest or even hint a way out!

integration of x*Sec(x)

If your Dad succeeds at this,Pls tell me the solution too!

- #6

well he has done a lot of things...he was a mathmatiton, he designs software, was an Engineer, has a masters in physics um...thats all i can think of at the time being.mattmns said:Do you need to understand the problem? What is your dad's background?

- #7

I don't know, witch is pretty stupid. If i eventuoaly find a question that stumps him and he says the rong answer he won't beleve that its rong. :grumpy:GCT said:how do you know your dad's answer is accurate, not necessarily bogus, but he might be off the mark

- #8

DaveC426913

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I can't get my father to acknowledge that there is no such thing as centrifugal force. He insists (or did 10 years ago) that the bucket on the string will go flying away at an angle instead of tangential to the circle.

Some day ... some day ... I will prove it to him. I will probe him wrong. I will prove them ALL wrong. They laughed at me. They mocked me. But I will show them. I will how them my POWER. They will flee, like ants under my feet. I will...

What? Is this thing still on? **

Some day ... some day ... I will prove it to him. I will probe him wrong. I will prove them ALL wrong. They laughed at me. They mocked me. But I will show them. I will how them my POWER. They will flee, like ants under my feet. I will...

What? Is this thing still on? **

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- #9

Mental Gridlock

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whozum

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"What is the purpose of meaning?"

-Dexter's lab

-Dexter's lab

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moose

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Mental Gridlock

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- #13

shmoe

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heman said:Well there is a question in Mathematics which My teacher asked me when i was in 11th class and i haven't come across anybody who could suggest or even hint a way out!

integration of x*Sec(x)

If your Dad succeeds at this,Pls tell me the solution too!

The integral of x*sec(x) cannot be expressed as an elementary function- meaning usual nice finite combinations of exponentials, logarithms, polynomials, trig functions, etc. This is the same situation as the more common e^(-x^2).

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Mental Gridlock

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BobG

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If you had a tunnel that went straight through the Earth from New York City to Tokyo and dropped an unpowered train in the New York end, how long would it take to roll to Tokyo (assuming the tunnel was a sealed vacuum and the Earth was stationary)? It would speed up until the tunnel reached the midway point between New York and Tokyo and then slow down at the same rate. It would take about 42 minutes for it to gently roll to a stop in Tokyo.

How about from New York City to Sydney Australia? About 42 minutes.

New York City to Los Angeles? About 42 minutes.

Even if he's not stumped, he'll at least enjoy explaining why.

This link, http://www.physics4all.co.il/open.php?link=628 [Broken], explains the problem. Just scroll down to "A Boring Problem".

Some of the other problems might give you some ideas, as well.

How about from New York City to Sydney Australia? About 42 minutes.

New York City to Los Angeles? About 42 minutes.

Even if he's not stumped, he'll at least enjoy explaining why.

This link, http://www.physics4all.co.il/open.php?link=628 [Broken], explains the problem. Just scroll down to "A Boring Problem".

Some of the other problems might give you some ideas, as well.

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- #16

yourdadonapogostick

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ask him for a valid argument of creationism :biggriN;

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marlon

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I made some quizzes here on PF, ask him these questions...just scroll down to the quizzes : https://www.physicsforums.com/journal.php?s=&action=view&journalid=13790&perpage=10&page=8 [Broken]Shippo said:

marlon

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honestrosewater

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Ask him what women want.

- #19

marlon

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Or ask him why there are only eight gluons ?

Or ask him who really invented heliocentrism

...check the quizzes

marlon

- #20

Mental Gridlock said:

sorry i phrased it rong insted of right it should be *correct. And yes he would be good on jepordy

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Mental Gridlock

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BobG

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That's too easy. Women want a man that can dilate his eyes at will.honestrosewater said:Ask him what women want.

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JonF

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money?honestrosewater said:Ask him what women want.

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arildno

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Why should I bother to learn how to dilate my EYES at will?BobG said:That's too easy. Women want a man that can dilate his eyes at will.

Yet another example of the inscrutable female psyche..

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Moonbear

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An optometrist? Well, yeah, they do make good money and work regular hours; not a bad choice.BobG said:That's too easy. Women want a man that can dilate his eyes at will.

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dduardo

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- #27

whozum

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- #28

dduardo

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whozum said:

Watch out, his head might explode.

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JamesU

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don't put him on jeopardy, put him on millionare. you pick: $20,000 or $1,000,000

- #30

honestrosewater

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Yeah, we really want someone with a huge e.g.o. anywayarildno said:Why should I bother to learn how to dilate my EYES at will?

- #31

heman

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shmoe said:The integral of x*sec(x) cannot be expressed as an elementary function- meaning usual nice finite combinations of exponentials, logarithms, polynomials, trig functions, etc. This is the same situation as the more common e^(-x^2).

I know its solution and i very well know its solution contain polylog function and other adhoc complex functions,but i don't care about the complexity involved!

Do you know how to solve it??

I have tried this question more than any question i can think of!

I don't agree with what you say about e^(-x^2)

Its a very easy question which can be solved trivially with the help of Polar Coordiantes and further with change of variables!

I guess you must have been pointing to x^x,its solution can't be written in form of elementary functions!

- #32

heman

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honestrosewater said:Ask him what women want.

Tell me what do you want??

- #33

honestrosewater

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If you have to ask, you don't really want to know.heman said:Tell me what do you want??

Hey, I'm getting the hang of this inscrutable psyche stuff

- #34

heman

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honestrosewater said:If you have to ask, you don't really want to know.

Hey, I'm getting the hang of this inscrutable psyche stuff

So...Hmmmm...Ok...Well ...Yeah

I have observed all through that women reveal only when they are asked!

- #35

shmoe

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heman said:I know its solution and i very well know its solution contain polylog function and other adhoc complex functions,but i don't care about the complexity involved!

Do you know how to solve it??

I have tried this question more than any question i can think of!

Write sec(x) in terms of exponentials, [tex]sec(x)=2/(e^{ix}+e^{-ix})[/tex], then a change of variables, [tex]e^{ix}=t[/tex]. Using partial fractions you can then write the integral in terms of dilog say, which is an integral you can't express in elementary terms. This isn't really anymore satisfying than the original form though, but I guess this is the find of thing you're looking for. I wouldn't call rearranging this integral into some other arbitrary looking integral, that necessarily has no elementary solution, "solving" anything, but that's just me.

Or if you like you can express x*sec(x) as a power series and integrate that (keeping mind of the interval of convergence). Again, this is somewhat unsatisfying and not in elementary terms (which implies a finite number of terms).

heman said:I don't agree with what you say about e^(-x^2)

Its a very easy question which can be solved trivially with the help of Polar Coordiantes and further with change of variables!

You can work out [itex]\int_{-\infty}^{\infty}e^{-x^2}dx[/itex] exactly by polar coordinates or other tricks. This is

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