Snow surfer

What type of software is used to make this video, a specific name would be useful http://youtu.be/JTj9AcwkaKM

I am reading a paper (econometrics/statistics) and there is notation that I don't understand.

It is w~MA(0) , where w is the variable. What does this mean? I haven't seen MA( .) Is it something like AR(1) meaning autoregressive with 1 lag?

thanks for the help

Le f be a function such that f(x+y)=f(x)+f(y) for all real x,y. Suppose lim as x goes to 0=L . Show that there exists a such that f(x)=ax for all x

I am trying to take the limit of :

n^(12) / ( n^13 - (n-3)^13) as n goes to infinity I need to prove it is 1/39

I cannot use derivatives or hopitals rule, I must treat it like a sequence.

I am trying to prove by induction 7*n^3 < 5^n for n=>4

My base case for n=4 is true but then for n+1 i am stuck

How to show 2*|ab|<= a^2+b^2 for any real a,b?

i know it is suppose to come from geometric mean is less than the arithmetic one but I can't link them

Then how to prove 4*|ab| *(a^2+b^2)<= a^4+6a^2b^2+b^4

I am currently on my last year of my undergrad . In Economics and Math minor. I would probably finish this degree. and start a new one next year.

I am thinking of going into engineering. Maybe chemical engineering.

Economics is just a little ridiculous. I am not interested in the formal models ,that are practically useless. I am only interested in Economic Development. Help the people to get out of poverty. Running experiments to see which policy works . Going to graduate school in economics would mean many years of study and my impact could be minimal. Publishing papers just to show one thing that might not be put into practice ,fitting curves to data or have policy suggestions ignored by governments.

As an engineer I could actually do things to change, help purify water in poor countries, find solutions to their problems really improve things.

As for time Getting a new engineer degree would take me 4 years, Economics grad school would take me at least 5 years so time is not an issue.

Any advice?

S and T are related by the following relationship . S=k/T , where k is a constant. If S increases by 50% by how much does T decreases? and vice versa if T increases by 50% how much does S decreases?

the answer is suppose to be 33.33% but I don't know why.

I need to multiply certain observations by a certain element of a matrix for certain years only

I wrote

gen labour_expenses=.

matrix define AWI= (34242\32423\..........) so the first entry is for year 1962 etc

forvalues i 1/50 {

replace labour_expenses = labour*AWI[`i',1] if fyear ==1961+`i'

}

it tells me

Invalid syntax for the loop ....why?

I still haven't figuered how to use Statalist for help sorry

Tavi drives 113 miles at 50 miles per hour and return via the same route at 60 miles per hour.

Quantity A: Tavi's average speed for the entire round trip

Quantity B : 55mph

IApparently the anser is B , but I don't get why ? i thought I could calculate the average speed by by

(113*50+113*60) / (2*113)= 55 mph.....but it isn't right why?

Can anyone tell me where I can confirm that in the US, firms can expense depreciation linearly?

Is this done a lot in firms?

This is for a research project.

a) A drawer contains n = 5 different and distinguishable pairs of socks (a total of ten socks).

If a person (perhaps in the dark) randomly selects four socks, what is the probability that

there is no matching pair in the sample

b) A drawer contains n different and distinguishable pairs of socks (a total of 2n socks). A

person randomly selects 2r of the socks, where 2r < n. In terms of n and r , what is the

probability that there is no matching pair in the sample?

so I know that there are 210 possible combinations, but not how to get the ones with no matching socks as well as b)

Compute the number of ten-digit numbers that contain only the digits 1,2,3 and where the digit 2 appears exactly twice.

I did the following but I don't know if its right, how should I approach this type of questions?

I thought that there are 9*9 ways you can move the 2s around and then in the 8 spots lefts you choose 1 from 1,3 so my answer would be 9*9*(2)^8 ?

Examining patients: they can have regular/irregular heartbeat and high/normal/low blood pressure

20% have high blood pressure; 30% have low blood pressure; of those with irregular heartbeat, one quarter have high blood pressure ; of those with normal blood pressure , 40% has an irregular heartbeat

A) What portion of the patients have an irregular heart beat AND low blood pressure

B) What portion of the patients have an regular heart beat AND low blood pressure

I tried using Bayes theorem and probability "identities" but I can't figure this out.

I just found the obvious and put in this table.

____ low____ normal___high

reg ________30% ________ |

irreg ________20% _______ |

total 30% ___50%____20% | 100%

so we know that P( high | irregular)= 1/4* P(irregular) but for some reason I don't seem to be able to use this information for anythig

Find the Inverse Laplace Transform

(7s+5) / (s^2+s+7)

Not just putting it in wolfram alpha.... I tried doing partial fractions. I completed the square in the denominator and then separated it but I can't seem to get it right

Find the Inverse Laplace Transform

(7s+5)/((s+1/2)^2+27/4) => I can't seem to make it work

I am having trouble finding the series solution for

e^(x) y''-xy'=0

I don't know how to deal with the exp(x)

Solve (2*exp(y)-t)y'=1

It seems that the answer is ln(t) but i cant get to it, i cant seem to get it into a form i can use integration factor or variation of parameters or something

Help with differential Equation question.

I can do the integration factor and exact equation part but how does one use parametrisation?

Here is the question :

Use parametrisation first, derive the equation including y and p =dy/dx

and use the ntegrating factor method to reduce it to an exact. Leave the solution in implicit parametric form.

y^3+ y^2= xy'y

I don't get this method for nonlinear ODES

example F(y,p)=0 y=ø(p) then dx=ø'(p)dp/p

x=Integral [ ø'(p)dp/p

another example is

x=p+sin(p/x) where p=y'=xt <=why??

then

x=sin(t)/1-t

p=t*sin(t)/1-t

dy=t sin(t) *[(1-t)cost+sint]/[1-t^3] dt <= where does all of this come from????????

so then we would integrate for y? what is this method with parameters I don't get it. Can I read about it somewhere?