Can someone help me with my math homework? (1 Viewer)

[PatB]

Still no solution. What a shame. The great minds of the HTF are at a standstill.

 

[Patrick Sun]

There should be 3 answers (or roots) to the problem.

 

[PatB]

Hey Patrick (good name, strong name) what did you get for the 3 roots?

 

[Bryan X]

Are these the three roots you got Patrick (give or take a decimal place)?

-1.9338
0.693195
1.74063

 

[Patrick Sun]

Yup. The trick is to learn how to solve polynominal equations, which I've forgotten how to do. I'm guessing this problem comes from this topic in class?

But for this one example, using a spreadsheet and just plugging in values to iterate to each root is simple enough.

 

[PatB]

But I think the solution is needed b/c they're trying to learn the process.
Although plugging into a program is a process of sorts that not what they're looking for.
Patrick, did you get it the result from excel too, or with old-fashioned elbow grease?

 

[NickSo]

.69318946 and 1.7406352 ; y > 0

Bryan has it right (im too lazy to 'trace' the negative root... lol thank goodness for my Graphing calculator... I am SO screwed for my math class...

 

[Leila Dougan]

If you want to know how to use Excel to solve it check out this page:

http://www.microsoft.com/education/?ID=solving

If you want to know how to solve it by hand check out this page:

http://mathforum.org/dr.math/faq/faq...equations.html

The cubic formula is quite complicated, but it's just algebra. Once you get the foruma and all the variables set up correctly, you just have to keep plugging away at it until you get it solved.

 

[PatB]

Thanks for the help, I need to take some time to look this page over. Hopefully I can make some sense out of this but this page looks like a good place to start. I knew I could count on the HTF brains.
Gracias.

 

[Dome Vongvises]

I was great in Calculus in high school, and I was great in Calculus in college. Oh why oh why didn't I become a chemistry major and take Cal II through IV.

Lesson here kiddies: you stay away from math, your mind will stagnate.

 

[Yee-Ming]

Sheesh. I got a B in Maths at A level, and even taught the stuff as a relief teacher in my old school thereafter before university, but since then haven't touched maths at all. So right now I have no idea at all how to solve that. :b

Hence, what Dome said.

 

[NickSo]

What grade are you in? Here, they dont expect (or teach) you how to solve cubic functions by hand...

 

[PatB]

It's for grade 12 level. Maybe it's a trick question.

 

[Denward]

I remember factoring cubic polynomials in the 12th grade (in 1981 ). I don't remember the process anymore, but it was simplified if you assume the roots are integers (i.e. if the teacher set up the problem so that the answers are integers). I agree with everyone's Excel answers for the 3 roots. Since the answers are not integers, you would have to reference Leila's post for the most general approach.

Is there a typo in the original problem?

 

[Justin Lane]

Leila's link to the math forum will work well. If for some reason you cannot understand the approach, Pat, I can scan and send you a different write up on solving cubic equations (don't want to scan and post here since it is copyrighted material).

Having taken Calculus I thru V in college for engineering, I can honestly say we never had to solve cubic equations by hand with non-integer roots. It is just too cruel, especially on an exam. When such a situation arises with a cubic or higher order equation, (quite often actually when dealing with the transfer function of a system to be controlled) I use my good friend Matlab or my trusty TI-89 to do the work.

J

 

[Seth--L]

I forget it, but there is a plug and chug formula where you take the integral to get the answers. However, since it's expected that you're going to use a calculator to solve this equation, the easiest thing to do is graph it an see where on the graph hits 0.

 

[Patrick Sun]

Yeah, I also had Calc I-V and Diff-Qs in college for my EE, and I didn't recall having to solve by hand anything over a quadratic equation to get to an answer. Now, solving multiple integals by hand on an exam are a different story...