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# Who here is good at math?

Discussion in 'Members' Lounge' started by cheese9988, Apr 4, 2007.

1. ### cheese9988Senior MemberVIP

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Anyone here good at math? I havn't used the quadratic equation in years and having a heck of a time trying to solve this.

The basic equation:
Rt=Ro * [1 + AT + BT^2]

I am trying to solve for T. I know Rt, Ro, A and B
If I simplified correctly:

Rt=RoBT^2 + RoAT + Ro

I would then take Ro and multiply it times B and then times A to simplifiy it again. Then use the quadratic equation. Problem is when I do this my answers don't come out correctly? Anyone see what I'm doing wrong?

2. ### MikeBergyBlah blah blah....

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You need to get your equation in the form

A(t^2) + B(t) + C = 0

Then

t = (-2B +/- sqrt( (B^2) - (4AC) ) ) / (2A)

Rt=Ro * [1 + AT + BT^2] ----> A(T ^2) + B(T) + ( 1 - (Rt/Ro) ) = 0

And so

T = -B +/- sqrt( (B^2) - ( 4A( 1 - (Rt/Ro) ) ) ) / ( 2A )

Note: +/- is read "plus or minus"

Last edited: Apr 5, 2007
3. ### klyphDismemberVIP

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4. ### MikeBergyBlah blah blah....

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Last edited: Apr 5, 2007
5. ### Citizen_InsaneSenior Member

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t = (-B +/- sqrt( (B^2) - (4AC) ) ) / (2A) (looks like you left off some parentheses there). Like Mike said, you need to get the left hand side of the equation to = 0, so you need to subtract Rt from the right side before applying the quadratic equation. (Should you people know this, this is really basic 7th grade algebra...)

6. ### KannedBeast

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I'm never going back to college.... NEVER!

7. ### asmallsolSuper Moderator

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if you think that looks hairy, take a look at fluid dynamics or or electronic properties of materials.

8. ### cheese9988Senior MemberVIP

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This is for work. There is a fourth order equation also, but I'm not even going to touch that. Thanks for the help, I'll try it tonight and see if my number come out right!

9. ### GSRCRXsiSuper ModeratorModeratorVIP

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until you take flight dynamics, or flight simulation/modelling, or calc 4 - differential eq's, you havent hit hard math yet.

we just started reviewing Laplace Transforms in my flight dynamics class before we get into its actual application for the class, god i hate them.

but for the kind of thing you are doing, just gt yourself a TI-89 and use the solve function. FTW!

10. ### asmallsolSuper Moderator

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werd, I don't do much stuff by hand anymore. I can move variables through equations, find trick ways to eliminate unknowns, but if it wasn't for a ti89 or some other type of math tool, I would be mathematically inept.

11. ### cheese9988Senior MemberVIP

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I havn't used that kind of math since college. The computers or procedures already have the problem solved for us. The project I'm working on now needs me to put in a set of coefficients for the device I calibrated, and then have the computer pull a value off of a reference meter, and then calculate the formula to come up with a result in real time.

12. ### cheese9988Senior MemberVIP

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+1 Not even engineers sit there and calculate all that by hand, they have the computer do almost all of the work.

13. ### MikeBergyBlah blah blah....

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Hooray for Laplace Transforms. I loved modeling a MSD system using simulink and matlab, but Laplace was essential for simplifying the equations of motion down to something that could be processed by matlab. And to the ti-89. We loving called it the 'integrator', while the ti-85 was called the 'interpolator' all through thermo. I miss undergraduate classes. Well, class in general. Ian, why are you taking flight dynamics? I thought you were mechanical eng?

14. ### MikeBergyBlah blah blah....

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fixed Depends on what type of engineering work you do. I have had to write simple programs to do the work for me, but I still need to know how everything works in order to use it.

15. ### cheese9988Senior MemberVIP

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What I ment. We use procedures for things all the time. But someone has to write them and if something goes wrong you still have to know how the thing works to fix it.

16. ### GSRCRXsiSuper ModeratorModeratorVIP

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im mechanical & aerospace engr major. the dual major gets me instate tuition

17. ### CRX-YEMSuper ModeratorModeratorVIP

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I'm taking Diff eq's right now, I'm actually enjoying it. man I haven't solved a 4th order system of equations in a long time, let alone remember l' hopitals rule, etc....

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