Locus and hyperbolic functions

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Homework Help Overview

The discussion revolves around the locus of a point defined by hyperbolic functions, specifically examining the equation \( x(4y^2 + b^2) = ab^2 \). Participants are analyzing the algebraic manipulation of expressions involving hyperbolic cosines and sines.

Discussion Character

  • Mathematical reasoning, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to rearrange expressions to isolate variables and apply the identity \( \cosh^2\theta - \sinh^2\theta = 1 \). Questions arise regarding the correctness of steps taken, particularly in the manipulation of equations and the quality of presented work.

Discussion Status

Some participants have provided feedback on the clarity of the original poster's work and pointed out potential errors in the algebraic steps. There is an ongoing exploration of the factors involved in the equations, with indications that progress is being made towards understanding the problem.

Contextual Notes

Participants have noted issues with the quality of the work presented, which may affect the clarity of the discussion. There is an emphasis on ensuring that each step in the algebraic manipulation is correctly represented.

synkk
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show that the locus of the point [itex]\left(\dfrac{a(cosh\theta + 1)}{2cosh\theta},\dfrac{b(cosh\theta - 1)}{2sinh\theta}\right)[/itex]
has equation x(4y^2 + b^2) = ab^2

working: http://gyazo.com/4c96af128d0293bce7f18029c2f54b0d
where have I gone wrong :(
 
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Your 5th and 6th lines each have the form <some expression> = 1. The second should have something other than 1 on the right hand side.
 
synkk said:
show that the locus of the point [itex]\left(\dfrac{a(cosh\theta + 1)}{2cosh\theta},\dfrac{b(cosh\theta - 1)}{2sinh\theta}\right)[/itex]
has equation x(4y^2 + b^2) = ab^2

working: http://gyazo.com/4c96af128d0293bce7f18029c2f54b0d
where have I gone wrong :(

I have to say that the image of your work is very poor quality. IMO, you are lucky that haruspex took the time to decipher your hard-to-read work. I'm sure that many others wouldn't bother.
 
haruspex said:
Your 5th and 6th lines each have the form <some expression> = 1. The second should have something other than 1 on the right hand side.

see below

Mark44 said:
I have to say that the image of your work is very poor quality. IMO, you are lucky that haruspex took the time to decipher your hard-to-read work. I'm sure that many others wouldn't bother.

Apologies, I thought it was fine.

working:

[itex]x = \dfrac{a(cosh\theta + 1)}{2cosh\theta}[/itex][itex]y = \dfrac{b(cosh\theta - a)}{2sinh\theta}[/itex]

rearranging x = ... for cosh theta:

[itex]cosh\theta = \dfrac{a}{2x - a}[/itex]
subbing this into y = ...

[itex]y = \dfrac{b(\dfrac{2a-2x}{2x-a})}{2sinh\theta}[/itex]
rearranging for sinh:

[itex]sinh\theta = \dfrac{b(a-x)}{y(2x-a)}[/itex]

now using [itex]cosh^2\theta - sinh^2\theta = 1[/itex]
[itex]\dfrac{a^2}{(2x-a)^2} - \dfrac{b^2(a-x)^2}{y^2(2x-a)^2} = 1[/itex]
[itex]y^2a^2 - b^2(a-x)^2 = y^2(2x-a)^2[/itex]
[itex]y^2a^2 - b^2(a^2-2ax + x^2) = y^2(4x^2 - 4ax + a^2)[/itex]
[itex]-b^2a^2 + 2ab^2x - b^2x^2 = 4y^2x^2 - 4ay^2x[/itex]

not sure where to go from here
 
synkk said:
[itex]-b^2a^2 + 2ab^2x - b^2x^2 = 4y^2x^2 - 4ay^2x[/itex]

not sure where to go from here
You're almost there. Just need to spot a factor.
 
haruspex said:
You're almost there. Just need to spot a factor.

spotted it, thank you.
 

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