quickQuiz #3 (maths or PC)

by quad • 20 Nov 2007, 22:02 • Journals
Solve for x:

2^(x^2)-(x^2+5x+229)*log_5(|x|) = 0

Where log_5 is the logarithm in base 5 and |x| is the absolute value of x.

Hint: there are two roots ;)
Comments
36
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cointozz 20 Nov 2007, 22:05
... and i get banned for posting german gg
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quad 20 Nov 2007, 22:07
some people seem to enjoy these tasks... what's wrong with them (the tasks) ? :(
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cointozz 20 Nov 2007, 22:12
on the one hand its wrong to post comments not everyone can understand and on the other hand your posting math tasks I dont understand. wheres justice in this world?
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azznr 20 Nov 2007, 22:07
I
DONT
CAARE!!

on 20/11/07, 22:07:21
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Spirea 20 Nov 2007, 22:10
I'll have a look at it when I finish my 3on3s
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quad 20 Nov 2007, 23:07
well?
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Spirea 20 Nov 2007, 23:22
I'll check it now, but I'm tired, so will go sleep soon
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Spirea 20 Nov 2007, 23:32
blah, make rather ones with algebraic solutions, I don't have any math program at home :p

maybe Newton iteration would do on paper, but too lazy for that now
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quad 20 Nov 2007, 23:43
I solved it with the bisection method in python, with 6 iterations you get 3 correct decimals... Newton could converge way faster...
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Spirea 21 Nov 2007, 09:37
f(x) = 2^(x^2)-(x^2+5x+229)*log_5(|x|)
f'(x) = 2^(x^2)ln2 + 2x*2^(x^2) - (2x+5)log_5(|x|) - (1/ln5)(x^2+5x+229)

I put x0 = 1

x1 = x0 - f(x0)/f'(x0)
x2 = x1 - f(x1)/f'(x1)
etc.

x1 = 1.014221978
x2 = 1.014059556

too lazy to test the other roots, too much writing for my TI-86 already :)
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quad 21 Nov 2007, 11:39
Wow, that is extremely fast convergence, might have something to do with the fact you've started at 0.014 away from one of the roots :)
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Spirea 21 Nov 2007, 12:44
aye, I was a bit surprised myself as well :)

where's your physics exercise :D ?
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quad 21 Nov 2007, 13:00
Tonight! (around 8-9pm GMT I guess, when most people are on crossfire)
I'm still thinking what to give :)
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silly 20 Nov 2007, 22:14
honestly, why do ppl have to learn such bullshit in school?
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mist3c 20 Nov 2007, 22:17
good question, i havent got the anwser yet :(
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im a tree 20 Nov 2007, 22:29
umm... to get a better job than you? who knows
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silly 20 Nov 2007, 22:45
dude are you livin in a dream world? where do you get better jobs for 1337 math skills? please. nobody will hire an a-grade geek instead of someone who maybe got a worse graduation but more life experience.

what jobs do you get with exceeding math skills? either you keep on counting digits in your basement or you do something else where youll never need to use this bs again.
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im a tree 20 Nov 2007, 22:53
what about someone who has a couple of PhD's in physics/engineering related fields?

still, I need one of these "real world" jobs until I get that far, thinking of working on my programming or web development
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wipeout 20 Nov 2007, 23:23
"where do you get better jobs for 1337 math skills?"
Banks, insurances pay good money for maths students with a focus on statistics.
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dce 21 Nov 2007, 12:17
u r an idiot.
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ENSJQM 20 Nov 2007, 22:46
why do people have to learn this useless bullshit to get a good job?
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HansoO 21 Nov 2007, 02:50
again, maybe guys who will be programmers or mathematicians at banks or huge organisations or something?

yes, they are needed in someway!
at least the guys who build bridges and buildings need to know some math-stuff afaik...but nowadays its all done by computer-programs -.-
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seQuo 21 Nov 2007, 00:09
"what do i need this for" is just the standard question in school if a pupil is too stupid to understand something.
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Deactivated7001 21 Nov 2007, 07:26
Probaly you won`t permantly need such a task. But what you definitely need is the ability to solve logical systems/problems.
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alhric 20 Nov 2007, 22:18
bah, nothx.
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im a tree 20 Nov 2007, 22:38
ok you got me here, I dunno

the 2^(x^2) totally fucked me over, havent learnt how to do it yet... im sure theres an easy way im overlooking but meh, to bsg
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quad 20 Nov 2007, 22:39
Technically, it's not that easy :)
And I wouldn't suggest doing an algebraic solution. Try going for the numeric value :)
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im a tree 20 Nov 2007, 22:50
well, im tired now

ill try and work out an answer in school tomorrow :P
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HellHammer 20 Nov 2007, 22:43
why log with base 5??? if base is e then it is izybash
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quad 21 Nov 2007, 00:02
Logarithm base change formula? Log_5(x) = Ln(x)/Ln(5)
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shkz 20 Nov 2007, 22:44
x1 = -611,88

x2 = -609.38

or am i 2 stoned ? :P
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quad 20 Nov 2007, 23:05
Close, but not really...
Should be in the range -3...+3
2 positive and 2 negative
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HellHammer 20 Nov 2007, 22:53
math teacher @ uni says that if you see smth like 2^x^2 together with log and plain x in the same equation, you either RUN or forget practical math and try to work up a number with your head that satisfy the equation.
it could be really helpful if x^2+5x+229=0 had some real roots so that it could be simplified to smth else but even that is not the case.

edit:
im so stoned right now
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quad 21 Nov 2007, 00:06
Yea, I've put 2^x^2 especially to suggest you to forget all your theoretical maths... Useless in a problem like this. So make your pick, and work your way up to the solution.

http://en.wikipedia.org/wiki/Root_finding

The roots to be found are:
2.69546472992
and
1.01406095269

If you want the negative ones as well:
-2.66119158172
and
-1.01471313956

Tomorrow I'll put a physics problem :)
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seQuo 21 Nov 2007, 00:12
uuh
puu likes physic problems^^
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quad 20 Nov 2007, 23:07
might work better... but i used python :)
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