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Mathematics 15 Online
OpenStudy (anonymous):

Let k(x) = (f(x))^−1. find k'(2) given a tangent line with points (5,2) and (2.1,5.3) and the line of f(x) hitting (5,2)

OpenStudy (anonymous):

zepdrix (zepdrix):

Hey there :) Hmm that first one is a little tricky.

zepdrix (zepdrix):

Do you get unlimited guesses? I wanted to test an answer and see if I figured it out correctly.

zepdrix (zepdrix):

I can explain it also, I just don't want to explain it if I did incorrectly :) lol

OpenStudy (anonymous):

I have 2 guesses left

zepdrix (zepdrix):

Ah ok :c well here is what I did.

zepdrix (zepdrix):

Mmm hold up I gotta rethink that >.< Grr tricky tricky.

zepdrix (zepdrix):

oh oh oh ok here we go... i think

zepdrix (zepdrix):

\[\Large\rm k(x)=\frac{1}{f(x)}\]Taking derivative gives us,\[\Large\rm k'(x)=-\frac{f'(x)}{f^2(x)}\]We can use the points given to evaluate f'(x), yes?

zepdrix (zepdrix):

\[\Large\rm f'(2)=\frac{5.3-5}{2.1-2}\]\[\Large\rm f(2)=5\]That should give us everything we need. Any confusion on that? :O

zepdrix (zepdrix):

The negative in the first problem looks like its indicating a `reciprocal`, not in inverse.

OpenStudy (anonymous):

ok i follow

zepdrix (zepdrix):

So run the numbers!! :) Tell me what you get before you throw it into the thing! :O You don't wanna burn guesses!

OpenStudy (anonymous):

what does f^2 of x mean just f(x) squared?

zepdrix (zepdrix):

Yah I was being a lil fancy, my bad.\[\Large\rm f^2(x)=\left[f(x)\right]^2\]

OpenStudy (anonymous):

would the answer be -3/25

zepdrix (zepdrix):

Yayyyy good job \c:/ That's what I'm coming up with also. Let's give it a try.

OpenStudy (anonymous):

moment of truth scared face

zepdrix (zepdrix):

XD

OpenStudy (anonymous):

you my friend are a savior praise (300 chant) Ah-oooo Ah-oooo

zepdrix (zepdrix):

yay team!

OpenStudy (anonymous):

thanks again greatly appreciate it.

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