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General => General discussion => Topic started by: mcgee9t2 on 09 December 2012, 16:39
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got an assignment that has to be submitted by midnight tonight, have it all done, but one question, and i cant for the life of me do it. i must have spent around 4 hours today and 2 or 3 yesterday trying to do it.
basically its a simoultanious equation.
"given: Va=Ra Ia + K1 N and Te=T0 + K2 Ia
Estimate coefficients for Ra, K1, T0 and K2."
started with the first given equation, got:
@10% 25 = 1.8 Ra + 950 k1
@20% 25 = 3.2 Ra + 900 k1
now i know its a simoultanious equation, and i know that i have to do the same with the 2nd given equation to get T0 and K2. however i havent done a simoultanious equation for years.
so far this is what ive got.
Divide equation 2 by Ia at 20%
25 /3.2 = Ra (900/3.2) k1
7.8125 = Ra + 281.25 K1
7.8125 - 281.25 K1 = Ra
and at that point i get stuck, anybody able to give me any pointers on were i go from here. had a look on google ect. but that just confused me more.
and before anyone says, we havent covered this is lectures, we have coverd the formulas but not simoultanious equations. we have no notes on this ect ect ect. my notes was the first thing i looked at, then i had a google, then asked my parents, then asked a few lads who i go to uni with and there all stuck on it too. this is litterally a last port of call. no im not wanting someone to work it out for me im happy with doing that, just pointers in the right direction cause at the moment ive done 6 hours of reading about them and scribbling things down but just cant get my head around it and seem to be going around in circles.
cheers
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Haven't done simul eqautions for years, and without digging out my old college stuff I won't be able to tell you!
Good luck my friend! :lipsrsealed:
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Not gone that far into it, but here are the types we've been doing for our engineering degree.
I will give you an example and talk through the process, then you can possibly adapt it for your equations to fit.
A simultaneous equations is basically just figuring out the two unknowns. Here the unknowns are x and y.
* Begin by rearranging your equations to follow the format ax + by = c
*Multiply the equation so the one of the unknowns has the same value in every equation.
*Add or subtract one equation from the otherto get rid of one unknown, and solve for the second.
*Substitute the answer into one of the original equations, and solve for the other unknown.
You can then check both answers.
First get your two equations one above the other, and number them.
(1) 4x - 3y = 11
(2) 3x + 5y = 30
Multiply 1 by 2, and 2 by 1,
(1) 4x - 3y = 11 (x3)
(2) 3x + 5y = 30 (x4)
=
(3) 12x - 9y = 33
(4) 12x + 20y = 120
Next step is to simplify. Both equations begin with 12x, so they equal the same, and cancel each other out.
Subtract equation 3 from equation 4
(5) 29y = 87
Then transpose out.
y = 87/29
y = 3
You then substitute the answer into the first equation, so;
4x - 3y = 11 becomes
4x - 3(3) = 11
4x - 9 =11
Then transpose again, so;
4x = 11 (+) 9
4x = 20
x = 20/4
x = 5
You can then make sure its right;
4x - 3y = 11
4(5) - 3(3) = 11
= 20 - 9 = 11!!!!!!!!!!
Hope this goes some way to explaining it for you mate, and hope you get it done! All the best!
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Spot on that sean. cheers mate. hopefully got it now.
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Well done Seanl, I could not work it out for the life of me :grin:
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=7?
Do I win? :grin:
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is this rocket science? :shocked:
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Brings back vivid memories Seanl :wink:
That does make a lot of sense now remembered it! :smiley:
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Unfortunately for me, thats just the simple stuff! I've done a bit of maths now, (transposition/logs/quadratics/simultaneous/complex numbers/trianges/linear graphs/polynomial division etc.......... as well as the standard ratios/volumes yadda yadda yadda.
Got the difficult stuff in May when I get back on to it! Bit of a break after xmas until then, so hopefully some down time in the car club! :cool:
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Unfortunately for me, thats just the simple stuff! I've done a bit of maths now, (transposition/logs/quadratics/simultaneous/complex numbers/trianges/linear graphs/polynomial division etc.......... as well as the standard ratios/volumes yadda yadda yadda.
Got the difficult stuff in May when I get back on to it! Bit of a break after xmas until then, so hopefully some down time in the car club! :cool:
Good luck I'm 15 years out the back of my Exams, the only thing I still use is trig good job too cos the rest has been lost through various brain farts and meltdowns :grin:
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Unfortunately for me, thats just the simple stuff! I've done a bit of maths now, (transposition/logs/quadratics/simultaneous/complex numbers/trianges/linear graphs/polynomial division etc.......... as well as the standard ratios/volumes yadda yadda yadda.
ditto. just simoultanious equaions are the one thing ive never been able to do.
Finally got it done though :D
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Glad you got it worked out in the end bud!
What you studying at uni then?
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Part time Electrical and electronic degree mate. what kind of engineering degree you doing?
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Same as you but only to foundation level. The navy wont put us through the full degree cos they would loose too many people once we complete our return of service after doing it! We come up about 30 points shy of the full degree, but we can top it up through Portsmouth uni or the OU on completion if our avarage is 75% or more. The marking system they employ guarantees that though. We just have to sign on for a 3 year return of service after completing the course, before we begin.