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# Can you get this differential? Watch

1. I need to show that the differential of 1/cosh^2(x) = -2sinh(x)cosh^3(x).

There has already been a couple of mistakes on this so this could be another mistake. Is it possible to get that differential?

Shouldn't the cosh^3(x) be to the power of negative 3?

I tired by rearranging cosh(2x) = 2cosh^2(x) 1-1 and by dividing sinh^2(x) + cosh^2(x) = 1 by cosh^2(x) and then substituting that in and trying to differentiate but I can't get the minus sign in front of the answer and the cosh to have a positive power of 3.

Is it possible to do this then?

Thank you
2. Let

Then

So the differential becomes:

Seems the book may have a typo
3. (Original post by Spungo)
Let

Then

So the differential becomes:

Seems the book may have a typo
See thats what I got one time, so thanks for your help
4. (Original post by Spungo)
Let

Then

So the differential becomes:

Seems the book may have a typo
Sorry, I think I spotted a mistake in your work. Is du/dx not -sinh(x),making the whole answer positive?
5. (Original post by claret_n_blue)
Sorry, I think I spotted a mistake in your work. Is du/dx not -sinh(x),making the whole answer positive?
No. unlike its trigonometric counterpart, the derivative of cosh is just sinh. if you are unconvinced, refer to the definition and differentiate.

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