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Kindakrof
Caldari
Cruor Frater
Coalition of Carebear Killers
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Posted - 2007.04.30 03:20:00 -
[1]
Edited by: Kindakrof on 30/04/2007 03:24:17
Allright. There's a maths test in 4 hours and i'm not prepared well enough. I've got the major part down but there is a part wich is totally absurd and makes no sense.
note: i'm just doing an old test now and this is the absurd part.
Let me show you.
Solve this equation : x4 - 16x¦ + 63 = 0
(the 4 here is supposed to be superscript)
Now we got solutions to this along with the test but i have no idea where it's coming from. see
he writes down : z = x¦ -> z¦ - 16 z + 63 = 0 (okay...)
then what the christ : (z-7)(z-9) = 0 -> Z = 7 z = 9 (WtF???!?!)
z=7: x¦=7 -> x = ¦√7
z=9: x¦=9 -> x= ¦√9
What the christ. Where do the 7 and 9 come from???
And there's another one similar.
Solve. √x-3 = x-5 ---- > x-3 = (x-5)¦
x-3 = x¦-10x+25 ----> x¦-11x+28=0
And then come the ******* numbers-out-of-nowhere again
(x-7)(x-4)=0
x1= 7 x2=4 (1 and for should be subscript.
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Shimakaze
Arcturia Starfleet
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Posted - 2007.04.30 03:41:00 -
[2]
Well...for the first question, you use subtitute x^2 with z because quadratic equations are easier to solve, then you just expand z after you have a solution. z = 7 and z = 9 because you want to solve (z - 7)(z - 9) = 0. So if z = 7, then (7 - 7)(7 - 9) = 0(7-9) = 0, similarly for z = 9. Basically you want to find a z such that the equation equates to zero, i.e. finding the root. Now you know z = 7 and 9, and z = x^2, solve for x, voila.
I'm cramming for my own final exam right now...so that's as far as I can take you 
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Kindakrof
Caldari
Cruor Frater
Coalition of Carebear Killers
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Posted - 2007.04.30 03:50:00 -
[3]
 Originally by: Shimakaze
Well...for the first question, you use subtitute x^2 with z because quadratic equations are easier to solve, then you just expand z after you have a solution. z = 7 and z = 9 because you want to solve (z - 7)(z - 9) = 0. So if z = 7, then (7 - 7)(7 - 9) = 0(7-9) = 0, similarly for z = 9. Basically you want to find a z such that the equation equates to zero, i.e. finding the root. Now you know z = 7 and 9, and z = x^2, solve for x, voila.
I'm cramming for my own final exam right now...so that's as far as I can take you
ok the problem is now how i know its (x-7)(x-9) and not (x-8)(x-10)
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Areconus
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Posted - 2007.04.30 04:00:00 -
[4]
Originally by: Kindakrof
Originally by: Shimakaze
Well...for the first question, you use subtitute x^2 with z because quadratic equations are easier to solve, then you just expand z after you have a solution. z = 7 and z = 9 because you want to solve (z - 7)(z - 9) = 0. So if z = 7, then (7 - 7)(7 - 9) = 0(7-9) = 0, similarly for z = 9. Basically you want to find a z such that the equation equates to zero, i.e. finding the root. Now you know z = 7 and 9, and z = x^2, solve for x, voila.
I'm cramming for my own final exam right now...so that's as far as I can take you
ok the problem is now how i know its (x-7)(x-9) and not (x-8)(x-10)
Look, one of the easiest ways to solve a simple quadratic is to say "what adds to get the middle term, and what multiplies to get the last term" In this case, -7 and -9 add to -16, and -7 and -9 multiply to get 63. Thats the fast simple way, but wont work if its not a perfect square. So, if you took (x-7)(x-9) and multiplied them out, you would see why it works.
You basically just multiply each term in the first part by each in the second partm like:
x*x = x2
x*-9 = -9x
-7*x = -7x
-7*-9 = 63
Then your left with x2 -9x -7x +63 
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Shimakaze
Arcturia Starfleet
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Posted - 2007.04.30 04:09:00 -
[5]
Also...if it's not immediately obvious to do what Areconus suggested, you can use the Quadratic Formula. Google it up 
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Areconus
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Posted - 2007.04.30 04:12:00 -
[6]
Yep, as far as i remember, thered 4 or 5 ways to solve quadratic equations
factoring (also martinsville method)
graphing
quadratic formula
completing the square
...something else i cant remember
but stick with factoring when you can, its the easiest and fastest way, aside from using a graphing calculator
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Kindakrof
Caldari
Cruor Frater
Coalition of Carebear Killers
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Posted - 2007.04.30 04:38:00 -
[7]
Ok, now all that's left is to go there and give my best.
FOR THE MOTHERLAND!!
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Zeonos
Amarr
Fairtrade Syndicate
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Posted - 2007.04.30 06:59:00 -
[8]
i believe in you :)... have no idea what all the numbers was though ;)
__________________________
i will get a new sig soon. |
Sakura Nihil
Tabula Rasa Systems
The Star Fraction
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Posted - 2007.04.30 10:11:00 -
[9]
Originally by: Zeonos
i believe in you :)... have no idea what all the numbers was though ;)
Oh quadratic algebraic equations...how I miss your simplicity  ...
Funny enough though, I actually solved an annoying complex determinant today using the quadratic formula, these formulas come back in some of the weirdest situations ever  .
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Kindakrof
Caldari
Cruor Frater
Coalition of Carebear Killers
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Posted - 2007.04.30 10:49:00 -
[10]
Originally by: Sakura Nihil
Originally by: Zeonos
i believe in you :)... have no idea what all the numbers was though ;)
Oh quadratic algebraic equations...how I miss your simplicity ...
Funny enough though, I actually solved an annoying complex determinant today using the quadratic formula, these formulas come back in some of the weirdest situations ever .
Once you get it down it becomes very simple. It's the remembering what to do that's hard.
Anyway i took the test and if everything i did was correct then i have a possibility on 9.2 out of 10.
I'm happy with that
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