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# core 3 differentiation differentiate tan^2y pls help watch

1. pls help me with part a....I tried quotient rule but I'm still not getting the answer

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2. (Original post by bubblegumcat)
pls help me with part a....I tried quotient rule but I'm still not getting the answer

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Are you given the derivative of y = arctan(x)?
3. Are there any other rules of differentiation you can think of that may help?
4. (Original post by SeanFM)
Are you given the derivative of y = arctan(x)?
do I need to know that? I was never taught that :s

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5. (Original post by lukejoshjames)
Are there any other rules of differentiation you can think of that may help?
I tried dy/du x du/dx(I think that's correct) and I got 2tanysec^2y but I'm not sure if that's right

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6. (Original post by bubblegumcat)
do I need to know that? I was never taught that :s

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It may help to find dx/dy using the chain rule and see where that gets you.

(Original post by bubblegumcat)
I tried dy/du x du/dx(I think that's correct) and I got 2tanysec^2y but I'm not sure if that's right

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There you go - so what does that equal to? And how do you get x back into the equation?
7. (Original post by SeanFM)

It may help to find dx/dy using the chain rule and see where that gets you.
oh i tried that I think...2tan y sec^2y is what I got..I'm not sure if that's correct?

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8. (Original post by bubblegumcat)
oh i tried that I think...2tan y sec^2y is what I got..I'm not sure if that's correct?

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Correct so far - now see my edit in the post above.
9. (Original post by bubblegumcat)
oh i tried that I think...2tan y sec^2y is what I got..I'm not sure if that's correct?

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What trigonometric identity relates and ?
10. (Original post by Zacken)
What trigonometric identity relates and ?
1 +tan^2 = sec^2?

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11. (Original post by SeanFM)

It may help to find dx/dy using the chain rule and see where that gets you.

There you go - so what does that equal to? And how do you get x back into the equation?
that would be 2tany/cos^2y right ?

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12. (Original post by bubblegumcat)
1 +tan^2 = sec^2?

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No.
13. (Original post by Zacken)
No.
how does that relate to this question? do I need to change tan^2y into sec^2y-1?

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14. (Original post by bubblegumcat)
that would be 2tany/cos^2y right ?

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That is still dx/dy but you've changed sec into cos, which can work but you don't need to do it.

Remember that dx/dy = 1/(dy/dx).

As Zacken is helping as well I will bow out.
15. (Original post by bubblegumcat)
how does that relate to this question? do I need to change tan^2y into sec^2y-1?

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No. You know that and you want an answer involving so you want to convert everything into .
16. (Original post by SeanFM)
That is still dx/dy but you've changed sec into cos, which can work but you don't need to do it.

Remember that dx/dy = 1/(dy/dx).

As Zacken is helping as well I will bow out.
ohhh I see, thanks!

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17. (Original post by Zacken)
No. You know that and you want an answer involving so you want to convert everything into .
got it, thanks!

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18. (Original post by bubblegumcat)
got it, thanks!

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Thank SeanFM. :-)

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