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Tricky hyperbolic function proof.

i) Show that (coth(x)+1)/(coth(x)-1) = e^(2x)


So,

coth(x) = cosh(x)/sinh(x)

cosh(x) = (e^(x)+e^(-x))/2

and

sinh(x) = (e^(x)-e^(-x))/2

Thus:

coth(x) = (e^(x)+e^(-x))/(e^(x)-e^(-x)) ------- A


I then replace the coth(x) in the original with A. But I can't seem to do anything with it..

I have been trying for 2 hours :colondollar: I've tried multiplying by all sorts of 1s with the intention of making things simpler.

Can anyone point me in the right direction?
Original post by Contempt
i) Show that (coth(x)+1)/(coth(x)-1) = e^(2x)


So,

coth(x) = cosh(x)/sinh(x)

cosh(x) = (e^(x)+e^(-x))/2

and

sinh(x) = (e^(x)-e^(-x))/2

Thus:

coth(x) = (e^(x)+e^(-x))/(e^(x)-e^(-x)) ------- A


I then replace the coth(x) in the original with A. But I can't seem to do anything with it..

I have been trying for 2 hours :colondollar: I've tried multiplying by all sorts of 1s with the intention of making things simpler.

Can anyone point me in the right direction?


Hint: Multiply your expression for coth(x) by exex\frac{e^{x}}{e^{x}}.
(edited 9 years ago)
Reply 2
Original post by alex2100x
Hint: Multiply your expression for coth(x) by exex\frac{e^{x}}{e^{x}}.


I had already tried that.. I got to the following expression:

Coth(x) = (e2x+1)/(e2x-1))

So the original becomes:

[((e2x+1)/(e2x-1))+1] / [((e2x+1)/(e2x-1)-1)]

But I dismissed it as I thought I'd taken a wrong turn.

What next?

I think my brain has melted to the point where I am missing something obvious..
(edited 9 years ago)
Original post by Contempt
I had already tried that.. I got to the following expression:

Coth(x) = (e2x+1)/(e2x-1))

So the original becomes:

[((e2x+1)/(e2x-1))+1] / [((e2x+1)/(e2x-1)-1)]

But I dismissed it as I thought I'd taken a wrong turn.

What next?

I think my brain has melted to the point where I am missing something obvious..



You get to this stage:

[((e2x+1)/(e2x-1))+1] / [((e2x+1)/(e2x-1)-1)]

Then the next step is to simplify this by adding the one on the top and taking the one away on the bottom.

I just did the problem and you will see if you do this the expression simplifies after you do this and you can get the required RHS
Reply 4
Ahh I got it.. Thank you kindly :smile:

+ rep
Reply 5
Original post by Contempt
Ahh I got it.. Thank you kindly :smile:

+ rep


You've got it now, but if you'd left your original expression in terms of cosh x / sinh x and then multiplied top and bottom by sinh x you might have found your task a lot easier :smile:

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