The Student Room Group

implicit differentiation

does x = sec 2 y differentiate to 2 dy/dx sec y tan y ?
Reply 1
Original post by smooo
does x = sec 2 y differentiate to 2 dy/dx sec y tan y ?


If you differentiate it with respect to x, sure.
Reply 2
Original post by Zacken
If you differentiate it with respect to x, sure.


thank you
Reply 3
Original post by smooo
thank you


np
Reply 4
Original post by smooo
thank you


Please ignore my previous post, I was busy and missed something. The correct expression (if differentiating w.r.t x) should be 2dydxsec2ytan2y2 \frac{dy}{dx} \sec 2y \tan 2y.

I'm incredibly sorry.
Reply 5
Original post by Zacken
Please ignore my previous post, I was busy and missed something. The correct expression (if differentiating w.r.t x) should be 2dydxsec2ytan2y2 \frac{dy}{dx} \sec 2y \tan 2y.

I'm incredibly sorry.


Don't worry about it
Reply 6
Original post by smooo
Don't worry about it


Thanks, so you can see that you get dydx=12sec2ytan2y\dfrac{dy}{dx} = \frac{1}{2\sec 2y \tan 2y} yeah?

But you know that sec2y=x\sec 2y = x and you know that 1+tan22y=sec22y=x2tan2y=x211 + \tan^2 2y = \sec^2 2y = x^2 \Rightarrow \tan 2y = \sqrt{x^2 - 1}.

So dydx\frac{dy}{dx} can be found as a function of xx.
Reply 7
Original post by Zacken
Thanks, so you can see that you get dydx=12sec2ytan2y\dfrac{dy}{dx} = \frac{1}{2\sec 2y \tan 2y} yeah?

But you know that sec2y=x\sec 2y = x and you know that 1+tan22y=sec22y=x2tan2y=x211 + \tan^2 2y = \sec^2 2y = x^2 \Rightarrow \tan 2y = \sqrt{x^2 - 1}.

So dydx\frac{dy}{dx} can be found as a function of xx.


thanks a lot, sorry for putting you through so much trouble.
Reply 8
Original post by smooo
thanks a lot, sorry for putting you through so much trouble.


no no it's my fault for not checking more carefully :tongue:

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