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## #1 Re: Help Me ! » proof? » 2012-05-29 00:07:32

Also, when adding vector fields like u+v
is it the same as when you add normal vectors?

say u=(ai+bj+ck)  and v=(di+ej+fk)   does u+v=(a+d)i+(b+e)j+(c+f)k ???

what is the graphic representation of adding vector fields?? Is it just adding every two vectors of the same co-ordinates together?

## #2 Help Me ! » proof? » 2012-05-28 23:57:29

nevinsmith
Replies: 1

Hi guys,

problem goes like this,
proof curl(u+v)=curl u + curl v

I assume u and v are 2 different vector fields... and have sufficient differentiability

Is there a way to do this without expanding the cross product?

## #3 Re: Help Me ! » eigen vectors » 2012-05-02 22:49:15

oops i mean for 4 it's [0;1] like a column vector

## #4 Help Me ! » eigen vectors » 2012-05-02 22:44:04

nevinsmith
Replies: 1

Hi guys,
I can't seem to find the eigen vectors for matix
[3 0;
3 4]

the answers says for eigen value 3 it's [-1;3]
4 it's [0,1]
I can find the eigen values but how do you solve the matrix multiplication
when the top row is made of zeros?

Also, does anyone know to use matlab? It's really pissing me off

## #5 Re: Help Me ! » How do you find the limits of convergence for a maclarin series? » 2012-01-30 21:01:15

Is it that the absolute value of the f(x) exponentialed term must be always be less than 1?

## #6 Re: Help Me ! » How do you find the limits of convergence for a maclarin series? » 2012-01-30 20:56:00

bobbym, thanks for helping me

I still don't entirely understand this,
'One way of knowing the radius of convergence is by your general knowledge of series. It is easy to see the when x>1 that series will not converge. Why, because the terms will not be getting smaller. Same thing for x<-1.'

How did you see that the series will not converge if x>1? is it like a guess and check thing?

## #7 Help Me ! » How do you find the limits of convergence for a maclarin series? » 2012-01-30 19:28:19

nevinsmith
Replies: 4

Hi guys, say that I want to expand ln(1+x) using maclarin series,
How do i find what limits the expansion will be valid for?

what if I use taylor series and center it around 1,2,3... etc

I know how to do the expansions and stuff but not really how to find what values of x the expansion will converge for.

## #8 Re: Dark Discussions at Cafe Infinity » what has tertiary education turned into? » 2012-01-16 16:19:26

hi bobbym,

Hmm,,, how do i quote? lol

You are right about how success isn't neccesarily defined in terms of wealth, but everyone has their own definitions for success.

For me personally, I would hate to live a normal man's life, I guess Jay Z's lyrics
'I rather die enormous than live dormant' describes my definition of success. A billionaire is just an expression for wealth, I would be quite happy with 150mil lol.

"it is not what you know but who you know."  So true, connections get you further in life than anything, but i just feels that people whos dumped so much money/loans into tertiary education should come out atleast better than working for minimum wage.

What I think could improve the current suituation is to increase the bench mark for university entrance and make the courses a lot harder, not in terms of money but in terms of academics so that only the elites who work hard can enter and graduate from university and therefore not be lumped into the same catagory as 'those who do not earn their degree' upon graduation.
At least then people won't waste money on further education when they do not need it.

Also, do you seriously use Taylor series as an engineer? I noticed that a lot of professors in engineering never really worked as an engineer, I'm just a first year student so don't extensively know the courses but prehaps they should switch degrees into teaching things with more practical use. When I graduated from highschool, I knew heaps about complex numbers but almost nothing about writing a CV, wasn't until i started looking for a job a month later that i really learnt it, and now I feel like I forgot everything about what i did learn in highschool.

## #9 Re: Dark Discussions at Cafe Infinity » what has tertiary education turned into? » 2012-01-15 22:07:17

Bobbym,
how is being well educated a bad thing?

Sorry if i anger anybody, just expressing my views on tertiary education being more profit driven.

Also, whats a 'decent person'? and how does wanting to be successful contradict that?

I grew up in a poor family, both my parents are immigrants working in minimum wage jobs, although i'm grateful for them, I'm sick and tired of not seeing any change, being deprived of success I strive for a better future. Is that so wrong?

Once again not trying to anger anyone,

But growing up you hear the saying 'study hard = good job', which may not neccessarily be true anymore.
Just my opinions

## #10 Re: Dark Discussions at Cafe Infinity » what has tertiary education turned into? » 2012-01-14 22:39:49

wow i didn't realise the s word was sensored to 'math' lol

## #11 Dark Discussions at Cafe Infinity » what has tertiary education turned into? » 2012-01-14 22:38:11

nevinsmith
Replies: 7

Hi everyone,
I'm from New Zealand and I work part time at MacDonalds, I'm also a full time university freshmen student.

One thing I realised is that there is quite a lot of fresh university graduates that work at the same
Mac Donalds as me doing the exact same thing being paid minimum wage. Is this kind of math happening
in the States? Fresh Bcom BA BSc graduates working at deadend jobs, and they have been there for like
a year.

Granted New Zealand is in quite an economic crisis right now, and jobs are hard to find. The older professionals are not retiring hence new professionals cannot find niches in society.

The share number of tertiary education providers in my country is astounding, for 4 million people we have about 7 universities and other polytechnics. Almost everyone thats graduating from highschool is now expected to attend university and this saturates the job market with an overabundancy of people with degrees.

Is it just me or has tertiary education became more of a profit driven industry, so the providers can drag the money out of students promising milk and honey at the end of the road only then do they arrive to work at macdonalds.

It seems to me that the only degrees worth doing are tech degrees like medicine, law or engineering while soft degrees such as arts and commerce just come out unemployed. And yet so many students choose to do those degrees as having a bachelors degree has become a minimum prerequesit for even low paid jobs such as call centres.

I've heard that a lot of engineering students (im doing chem-eng) are also graduating unemployed, unless you're an honours student. Is it really that bad? I want to finnish my degree maybe a masters to the best of my abilities and hopefully move to the states. Is unemployment for engineers a serious issue in the States? do companies hire foreigners?

what are your opinions on this? am i the only one thinking that people are suckered into doing useless degrees or forced into it because everyone else has one?

Also, don't laugh but my life goal is to be a billionaire, I'm hoping to start a business probably in the engineering field once i'm out of college and have some work experience/money. So anyone got any advice for a young and foolish person but filled with dreams and ambition like me? Should I be focussing on education right now?

You are all an educated bunch hence I think this is quite a good question to ask here! thanks

## #12 Re: Help Me ! » high school complex numbers » 2011-12-30 21:24:14

this question i got stuck at the part where you factorise out y-k

in suituations like this how did you factorise that?
any special methods or just lots of practise

## #13 Re: Help Me ! » high school complex numbers » 2011-12-30 21:22:02

hi bobbym,

so they are,
-rt2+rt3i
-rt2-rt3i
rt2-rt3i
-rt2-rt3i
rt2-rt3i

with 2 of the roots being repeated?

## #14 Re: Help Me ! » high school complex numbers » 2011-12-30 20:41:03

http://www.nzqa.govt.nz/assets/scholarship/2011/93202-qbk-2011.pdf

it's question 5b

Im going to be doing chemical engineering, hope the maths don't get too crazy in university
XD

thanks to everyone

## #15 Help Me ! » high school complex numbers » 2011-12-30 18:58:40

nevinsmith
Replies: 21

Hi, this question was in the 2011 new zealand calculus scholarship paper,

couldn't do it, don't know the answer,

x^6+(2-k)x^4+(25-2k)x^2-25k=0

given c=2^0.5+i3^0.5     ^o.5 are sqr roots
is one of the solutions of x.

find the other 5 roots.

thanks

## #16 Re: Help Me ! » how do i integrate this? » 2011-07-24 00:56:53

Hi Gar,

wow thank you so much!
thats so genious i would never think of that lol

thanks for the solution man!

## #17 Re: Help Me ! » probability question binormal distribution » 2011-07-24 00:52:36

hi bobbym,

How did you do it?

I took the sums of probability of more than 12 people (12,13,14...19) multiplied by the probability that the specific person won't get one of the 12 steaks (1/13, 2/14, 3/15 etc)
then 1-Ans
comes pretty close to the actual answer

Is there a shorter way? The exam allocates 40min for binormal distribution and there is no way i can answer this one in less than 10min lol

thanks for the help so far

## #18 Re: Help Me ! » how do i integrate this? » 2011-07-24 00:44:53

This is what i can get up to

int xSinx^3 dx

set u=x  u'=1

v'=sinx^3    integrate, v= cosx-1/3cosx^3

then integrate by parts

=xcosx-1/3xcosx^3 - int (cosx-1/3cosx^3)

i can't et rid of the integral!!

## #19 Re: Help Me ! » how do i integrate this? » 2011-07-24 00:31:22

hi gar and bobbym thanks for helpin guys

I still can't do it

can you please show me step by step how to integrate?
using integration by parts? i can't seem to get rid of the integral it keeps getting bigger and bigger

do i set u' as (sinx)^3 or as x

## #20 Re: Help Me ! » probability question binormal distribution » 2011-07-24 00:23:17

alright, this is the question word by word

A small restaurant seats 20 diners, and is full everynight. The chef knows from previous
experience that 40% of diners order steak. So she always has 12 in her fridge at beginning
of each night.
a customer can only order one steak maximum.

If a customer orders steak, what is the probability that he/she will recieve one?

## #21 Re: Help Me ! » how do i integrate this? » 2011-07-24 00:19:12

oh right, but i still can't solve it

how do i integrate x(sinx)^3

techniques i've taught are- integration by parts, substitution, trignometric substitution, partial fractions and i think thats it

## #22 Re: Help Me ! » probability question binormal distribution » 2011-07-24 00:10:42

to Gar '40% tables will order a steak means, even if there are 20 tables only 8 steaks will be ordered and everyone gets one!'

thats not quite true, not 40% of tables, each table has 40% chance of wanting to order one.
so there is a probability that all tables will want to order one

## #23 Re: Help Me ! » how do i integrate this? » 2011-07-24 00:04:21

could be a print error though

does the other one work out to be 2pi/3?

## #24 Re: Help Me ! » how do i integrate this? » 2011-07-24 00:03:06

no it's not x(sinx)^3 or xsin^3x

it's xsin(x^3) brackets present in the question and x^3 inside the bracket

## #25 Re: Help Me ! » probability question binormal distribution » 2011-07-24 00:00:34

basically, there is a probability of 40% that any table will order steak everynight. only 12 steaks are available at any one night. Given that someone orders strak, what is the probability that he will recieve a steak (they haven't ran out)

I think i actually solved the problem lol but it's just the aweful rounding.

anyway calculus is going good. thanks guys!