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Mathematics 18 Online
OpenStudy (el_arrow):

tan^-1(x^2y)=x+xy^2

OpenStudy (el_arrow):

find dy/dx by implicit differentation

OpenStudy (el_arrow):

i don't get what to do with the left part

OpenStudy (mathmale):

First, a bit of review: What is the derivative of the inverse tangent function?

OpenStudy (el_arrow):

sec2x

OpenStudy (el_arrow):

right?

OpenStudy (mathmale):

x^(2y) is, I assume, the argument of the inverse tangent function. Is that correct? to answer your question: 1) sec2x means sec (2x). No. What you need and want is 2) (sec x)^2. Big difference.

OpenStudy (el_arrow):

its x^2*y

OpenStudy (mathmale):

Your left side, tan^-1(x^2y), apparently stems from:\[\tan ^{-1}x ^{2y}\] Am I correct here? If not, DRAW the problem statement.

OpenStudy (el_arrow):

yes thats correct

OpenStudy (mathmale):

Please note that what I typed is not the same as your x^2y. It's worth spending the time to check and double check that you have presented the original problem correctly. I'd suggest you learn how to use equation Editor and Draw, if you haven't already.

OpenStudy (mathmale):

so now we've reviewed the derivative of tan x, and the correct result is (sec x)^2.

OpenStudy (mathmale):

That's the derivative with respect to x. Now suppose instead that you want the derivative with respect to x of tan u. What would that derivative look like?

OpenStudy (mathmale):

Hint: because 'u' is a separate function of x, we MUST use the Chain Rule here.

OpenStudy (el_arrow):

just looked through my notes and found that the derivative of tan^-1x is 1/1+x^2

OpenStudy (mathmale):

I'm very sorry; you are right.

OpenStudy (el_arrow):

so i multiply that times x^(2)*y

OpenStudy (mathmale):

\[\frac{ d }{ dx }\tan ^{-1}x=\frac{ 1 }{ 1+x^2 }\]

OpenStudy (el_arrow):

|dw:1411006936062:dw|

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