Math Is Fun Forum

Johnathan1

Member

Registered: 2006-06-10

Posts: 7

Past exam paper!!!!

Hello everyone, just a question to ask.....

Determine which quantity or combination of quantities you would plot on the x and y axis in order to plot a straight line and thus determine the constant c in the following question. (f, r are variable and c, b are constants). we need to identify x, y and c.

a) f^2 = c / (r^3)
b) f = L^-rc
c) f = rl^-c
d) f = cr - b
e) f = c/r - b

Ok i dont need the solutions, but if u could guide how i need to do this then that should be more than enough. If i have problems i will come back to u, thanks alot!!!!

polylog

Member

Registered: 2006-09-28

Posts: 162

Re: Past exam paper!!!!

What do you mean by 'combination of quantities' ? I mean, are you allowed to combine expressions of the parts (a) to (e) together with operators?
Or are you just supposed to identify which of these parts has a straight line graph?
If it is the latter, then only (d) is a straight line. (b) is an exponential curve, (e) is a hyperbola, and the others are other non-linear graphs.

Johnathan1

Member

Registered: 2006-06-10

Posts: 7

Re: Past exam paper!!!!

Ok thanks for that, i understand until this point......but how could i now find out c???

polylog

Member

Registered: 2006-09-28

Posts: 162

Re: Past exam paper!!!!

Well I'm not sure, it seems to me that the constants c are arbitrary, meaning that whatever we set them to, we will get an identical curve, but shifted up or down by the amount c.

For example the equation  f = cr - b  defines a "family of lines", and unless you are given some specific points that a specific member of this family must cross, it is not possible to solve for a specific c.

If we knew for example that f must pass through (1, 2) and (3, 4),  then
c - b = 2
4 = 3c - b

and we could solve these to get theconstants. But we don't know any specific points at all here, so I don't think we can solve for specifc constants.
Unless I'm not understanding the question correctly, in which case hopefully someone else can help.

Johnathan1

Member

Registered: 2006-06-10

Posts: 7

Re: Past exam paper!!!!

hey polylog, i just got to know this question was from error analysis......maybe that helps someone???? but anyway thanks for ur time on this question, i will try ur method.

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: Past exam paper!!!!

Is L a constant or a variable??

---

igloo myrtilles fourmis

Johnathan1

Member

Registered: 2006-06-10

Posts: 7

Re: Past exam paper!!!!

well i looked at the question again and it doesnt say anywhere if it is a constant, so it must be a variable probably?

Last edited by Johnathan1 (2006-10-07 08:43:53)