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#1226 Re: This is Cool » projectile motion » 2006-06-08 03:48:19

Get the vector function of t  for target
At t=0, target (a,b)
suppose the target velocity is (p,q), where q/p=tanθ
then the function is
(a,b)+t(p,q)= (a+pt,b+qt)
then get distance function, which means distance from where arrow is shot.
d(t)=√[(a+pt)²+(b+qt)²]

s(t)=wt, where w is the SPEED of the arrow. No matter at what angle it was shot, after time t, it is wt far from shot point.

√[(a+pt)²+(b+qt)²]=wt

#1227 Re: This is Cool » projectile motion » 2006-06-07 16:28:24

too long...
I think a way to solve your problem is like this
find the function of target distance from origin at time t
d(t)
find the displacement of the arrow after time t
s(t)
solve
d(t)=s(t)

solved t is hitting time
Now that you've got t, you know the position of the target when hitted, thus you'll find an (several) angle(s).

#1228 Re: Help Me ! » Probably the Chain Rule » 2006-06-07 16:04:05

Increasing at 0.24 per second.

#1229 Re: Help Me ! » Probably the Chain Rule » 2006-06-07 15:57:00

name g=g(R) a function that g(R)=1/R . Also g=f(x,y,z)=1/x+1/y+1/z
dg=d(1/R)
as well as
dg=d(1/x+1/y+1/z)
solve
d(1/R)=d(1/x+1/y+1/z) out

Or to be more rigorous:
you need to get R[sub]x[/sub] (

) and R[sub]y[/sub] and R[sub]z[/sub]
To get R[sub]x[/sub]
first get g[sub]x[/sub] and g[sub]R[/sub]
then using a theorem ( I cannot remember its name)
R[sub]x[/sub]=g[sub]x[/sub]/g[sub]R[/sub]
Similarly you can solve R[sub]y[/sub] and R[sub]z[/sub] out and make a dR

The first approach is Leibniz's approach, the second is traditional differential approach, and they get a same answer, some guy may have proved they are equavalent. Leibniz claimed using d notation may simplify algebrac manuplicion, he was great, wasn't he?

#1230 Re: Help Me ! » graphs slid around with subtraction » 2006-06-07 15:38:47

Proof of the assumption
--I discovered no knowledge about solving a polynomial solution is needed

the proof before assumpition IMPLIES that f(x-a)=y[sub]0[/sub] has no less solutions than f(x)=y[sub]0[/sub], for there is a solution for f(x)=y[sub]0[/sub], there exists a corresponding one for f(x-a)=y[sub]0[/sub].

This is a corollary from the x[sub]i[/sub] and x[sub]i[/sub]+a theorem.

Note this corollary applies to any a and any function.
Name f(x-a)=g(x)
t=x-a
f(t)=g(t+a)
t=x
f(x)=g(x+a)=g(x-(-a))
Using the corollary,
g(x-(-a))=y[sub]0[/sub] has no less solutions than g(x)=y[sub]0[/sub]
that's analogous to say f(x)=y[sub]0[/sub] has no less solutions than f(x-a)=y[sub]0[/sub]

Together, f(x)=y[sub]0[/sub] and f(x-a)=y[sub]0[/sub] has the same amount of solutions, assumption PROVEN!
smile smile smile
Should I go to  a math journal. Or was I doing some already-done work?

#1231 Re: Help Me ! » graphs slid around with subtraction » 2006-06-07 15:20:33

Another proof about g(x,y)=0 qualified for shifting rule

first about f(x)=y
f(x[sub]0[/sub])=y[sub]0[/sub]
then f(?-a)=y[sub]0[/sub]
The question here may seem to be solving an equation out. But not so.
First, x[sub]0[/sub]+a is qualified,
for f(x[sub]0[/sub]+a-a)=y[sub]0[/sub]
Second, every x satisfying f(x)=y[sub]0[/sub] can be grouped into {x[sub]i[/sub]}
then for each i, or each x[sub]i[/sub]
f(x[sub]i[/sub]+a-a)=y[sub]0[/sub]
here we proved x[sub]i[/sub]+a are qualified solutions for f(x-a)=y[sub]0[/sub], but are they all solutions? Is there a solution out of {x[sub]i[/sub]+a}? If there is one, the shifted function may have one more point at the altitude y=y[sub]0[/sub]

IF y[sub]0[/sub]=f(x) and y[sub]0[/sub]=f(x-a) has the same number of solutions, {x[sub]i[/sub]+a} is the complete solution set for f(x-a)=y[sub]0[/sub].

The assumption is what I cannot prove. But if anyone prove it, or has proved it, the proof is complete. Or to put it inanother way, now that f(x)=y can be applied by shifting rule, the assumption should be true.

The proof for g(x,y)=0 is the same. the same projection. the difference is minor.
for any x[sub]i[/sub] satisfying g(x,y[sub]0[/sub])=0
x[sub]i[/sub]+a satisfy g(x-a,y[sub]0[/sub])=0.

IF g(x,y[sub]0[/sub])=0 and g(x-a,y[sub]0[/sub])=0 have the same amount of solutions, the shifting rule applies.

I think the shifting rule can also be applied to inequality like g(x,y)≤0 because equalities and inequalities have tight connections. However, strict proof need rigorous knowledge on inequality theorems. So I assume it.

#1232 Re: Help Me ! » graphs slid around with subtraction » 2006-06-07 14:50:32

shifting rule can also be applied to
f(x,y)=0

Because:
Break the curve into very small pieces. Locally, you will solve out {y=g[sub]i[/sub](x)}, get one to one functions, and then you just need to connect them together.
Now the altogether f(x,y)=0 is ready for shifting rule.

Accually, that's how the theorem about implicit differential works.

#1233 Re: Help Me ! » graphs slid around with subtraction » 2006-06-07 02:59:58

that doesn't matter, the shifting rule is not limited to functions.

for post 4, Ricky, I recommand you  using x[sub]1[/sub] and x[sub]2[/sub] instead of both xs, to make it clearer.

post 2 is very clear.

I think the shifting rule also applies to x²+y²≤4 and (x-.5)²+(y+1.5)²≤4 as well.

#1235 Re: This is Cool » Question about Infinity » 2006-06-07 02:38:41

a single point infinitesimal of universe..
I don't know if this holds or not, but I do know around two thousands years ago, there was a great philosopher as well as a excellent logician who challenged space is made of infinite infinitesimals. His name was Zeno.

I wish String Theory may some day prove time and space together is made of sufficient simals instead of infinitesimals. And I wish I be alive that day. big_smile

#1236 Re: Help Me ! » mathematical induction qu » 2006-06-07 02:28:32

check the fractual containing both leftside and rightside



do you get a hint?

#1237 Re: This is Cool » Question about Infinity » 2006-06-06 18:48:13

Ricky, you see. That's why I tend to be conservative about infinity and would rather treated as a variable but not a reached thing. To think it as stable is natural, but that brings along too many bugs.

#1238 Re: Help Me ! » Vector Space and Subset » 2006-06-05 03:10:30

I happened to study matrix theory for a time.
Here goes Gram Schmidt process :

you have say 3 linearly independent vectors at hand.

first, get equivalent 3 orthogonal vectors. equivalent here means any of this 3 can be expressed as an linear combination of that 3, vise visa.

the first vector would be a trival one from the oringinal 3, this vector can surely be expressed as a linear combination, and the coefficients would be 2 zeros and 1 one.

then find a second vector, this vector should satisfy 2 conditions- a linear combination of the original 3, and orthogonal to the first one.

To Make things easier, only another original vector is added to the combination, which means one coefficient of the linear combination is 0.

The big step is to find the proper coefficients for the second one.
Define <α[sub]1[/sub] ,α[sub]2[/sub], α[sub]3[/sub]> as the original independent but not orthogonal vectors.

the first new vector built is β[sub]1[/sub] =α[sub]1[/sub]
=α[sub]1[/sub] +0α[sub]2[/sub] +0α[sub]3[/sub]

the second one β[sub]2[/sub] = α[sub]1[/sub]+kα[sub]2[/sub], the reason for only 1 indetermined coefficient is that given one orthogonal vector, any vector parellal to it is also orthogonal to the given one, and that 1 coefficients is simplier than 2 coefficients.

   ( β[sub]1[/sub] , β[sub]2[/sub])

=  (α[sub]1[/sub] , α[sub]1[/sub]+kα[sub]2[/sub])

= (α[sub]1[/sub] ,α[sub]1[/sub]) + k(α[sub]1[/sub] ,α[sub]2[/sub])

=0

just solve k out. Note (α[sub]1[/sub] ,α[sub]1[/sub])is just a simple number like 2, 46.5, etc.

now add the 3rd.
β[sub]3[/sub] =β[sub]1[/sub] +m β[sub]2[/sub] + n α[sub]3[/sub]
(A beginner or a poor mem person like i may think about alpha combination. we will find out why not quite soon)

This time the 3rd vector should be orthogonal to both of the previous ones
in order that 1-2 orthogonal, 1-3 orthogonal, 2-3 orthogonal.

(β[sub]3[/sub] , β[sub]1[/sub])=0 and (β[sub]3[/sub] , β[sub]2[/sub])=0
the first equation:

(β[sub]3[/sub] , β[sub]1[/sub] ) 

=  (β[sub]1[/sub], β[sub]1[/sub]) +m (β[sub]2[/sub], β[sub]1[/sub]) + n (α[sub]3[/sub], β[sub]1[/sub])

= (β[sub]1[/sub], β[sub]1[/sub]) +0 + n(α[sub]3[/sub], β[sub]1[/sub])

Here  the 0 idendity simplifies the equation make solution determined, that's why to choose as many βs as possible, and only one α at one time.

n will be easily solved, so be m.

#1239 Re: Help Me ! » infinitesimal values questioned. » 2006-06-04 13:12:52

big_smile
My dictionary say dude means playman, but I find dude a common address.

#1240 Re: Help Me ! » law of sins » 2006-06-04 13:09:08

cscθ   = 1/sinθ
multiply both sides by sinθ

#1241 Re: Help Me ! » trigonometry » 2006-06-04 13:07:27

devide the angle by half, and the devider will be orthogonal to the base, since two waists are equal(to 7).

#1242 Re: Help Me ! » Vector Space and Subset » 2006-06-04 13:05:17

you can not express any of the 1,t,t²,...,t[sup]n[/sup] as a linear combination of others, thus according to a theorem, they are linearly independent.

then we should check whether they are orthogonal one by one, and if they are unit vectors.

However, I find (1,t[sup]2[/sup])= (1[sup]3[/sup]-(-1)[sup]3[sup])/3≠0

to find symbols, see top blue bar

#1243 Re: Help Me ! » A integral problem » 2006-06-03 21:22:56

is there an "i' instead of a "j"?

#1244 Re: Help Me ! » ... equation ... » 2006-06-03 21:18:52

I don't know real infinity thing, what i know is an amount divided by a small number.

I find a case. do you think there is too much difference between enjoying Bill Gates' fortune and owning Warrant Buffet's investment?

Besides, it's not me who proposed infinity is an answer.

Anyway, to Raulito, if you accept some error and do not persuit absolute accuracy, there are accepted solutions.
Otherwise, there is none.

#1245 Re: Help Me ! » infinitesimal values questioned. » 2006-06-03 21:05:35

krassi_holmz wrote:

I have to aknowledge i can't really understand the infinitesimal (although I use it).
Here's my question-is it well-defined - does it REALLY exist?
How can a number be greater than infinity?

It's up to you, dude.

If you believe, it exists.

If you don't, it does not. tongue

#1246 Re: This is Cool » The reason why x/0 = no solution. Simply put. » 2006-06-03 01:50:30

It seems Ricky's solution is a defined version with a same core...

#1247 Re: Help Me ! » ... equation ... » 2006-06-03 01:43:15

krassi_holmz wrote:

For the limes thingy:
If

,
that doesn't imply:

and...again...NO SOLUTION!!!
(If there was some limmy solution, then all math theory would have been contradictory-and this would have been TERRIBLE!!)

No perfect solution.

But accepted solution. If you find a 0 on a calculator display credible for 0. Then there are many answers.

#1248 Re: Help Me ! » infinitesimal values questioned. » 2006-06-03 01:34:39

The way I understand it, infinitesimals are part of hyperreal numbers.  They are numbers which are smaller than any real number.  Because of this, I don't believe there is any way to express them besides through the use of symbols.
---------------------
It was Thomson's Idea, he created the Analysis on Infinitesmall in the midth of last century.(Sorry I can't tell the detail and I may have some errors)

However, his idea did not put a solution for dispute on infinity thing in mathematic society, and, not well accepted.

Here's perhaps a reason-
Since after any differentiation or integration, the result is derived from limit theory, every result can then be expressed as the original result plus a infinitesmall(number form), or minus a infinitesmall, or 2? or 3? so the result is subjective to a mathematician's favor.

Standard Defination of Infinitesmall is just as krassi said, a variable that can be as small as you want, given the endogenous variable it depends on can change in some way.

This defination is invented by French mathematician Cauchy- it's odd, but it never fails. The reason why it's so orthogonal is that it claims least assumptions but solves most limit problem. It has a very delicate logic inside, that it  doesn't claim any new defination, that it just said "IF" the endogenous variable can change in a certain way, which is left with doubt.

Whether the condition is finally satisfied is a big question, it involves whether dt in ds/dt can reach null, or a line can be cut into REAL infinite segments(points), or an area can be made of infinite line segments.

And that need pure mathematic assumption and defination.

I'm for the impossibility for the condition, and for approximation view, and also, for Cauchy's defination.

#1249 Re: Help Me ! » Differential Equation » 2006-06-03 01:04:06

That's it!
But how can i learn complex functions and differentials? What kind of books?
I'm eager to learn it,  could you recommand me a book on this kinda stuff? thanks roll

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