Need help from the math wizards!

[White Widow]

What is the derivative of:

f(x) = ß1ln(x) + ß2(ln(x))^2

is it:

f(x)' = ß1/x + 2*ß2ln(x)

???

Thanks!

 

[rgwalt]

Originally posted by: White Widow
What is the derivative of:

f(x) = ß1ln(x) + ß2(ln(x))^2

is it:

f(x)' = ß1/x + 2*ß2ln(x)

???

Thanks!

You forgot to do the chain rule in the second term. The second term is B2*y^2 where y = ln(x). So the derivative of the second term is 2*B2*y*y'. So the second term should be 2*B2*ln(x)*(1/x).

R

 

[White Widow]

Right you are...that's what happens when I try to do math I never really learned at 3AM.

Thx,
Aaron

 

[BigJ]

I'm actually glad when people post questions like this. It shows they're actually trying to work on a problem and figure out how you arrive at the solution rather then plugging it into a Ti-89, Maple, or Mathematica to get a solution.

 

[BigPoppa]

Originally posted by: BigJ
I'm actually glad when people post questions like this. It shows they're actually trying to work on a problem and figure out how you arrive at the solution rather then plugging it into a Ti-89, Maple, or Mathematica to get a solution.

I did that in high school. Then I got to college and almost got owned when I couldn't do simple stuff like the chain rule. Now my single variable (have yet to reach calc3) integral and derivative skills are excellent thanks to only using a simple 2 line TI scientific calulator.

 

[rgwalt]

My TI-92 was a great tool back in high school and early college calculus as it let me check all my work. However, I grew beyond it, and these days the programs that take derivatives for you are rarely helpful in my area because they won't simplify expressions to the form necessary to see the solution.

R

 

[BigJ]

Originally posted by: BigPoppa

Originally posted by: BigJ
I'm actually glad when people post questions like this. It shows they're actually trying to work on a problem and figure out how you arrive at the solution rather then plugging it into a Ti-89, Maple, or Mathematica to get a solution.

I did that in high school. Then I got to college and almost got owned when I couldn't do simple stuff like the chain rule. Now my single variable (have yet to reach calc3) integral and derivative skills are excellent thanks to only using a simple 2 line TI scientific calulator.

When I took Calc II in college and a lot of people didn't know how to do simple derivatives or integrals because they relied on calculators for the AP exam, it was liked OMGWTFPWNED for all those people come test time.

 

[chuckywang]

Originally posted by: White Widow
What is the derivative of:

f(x) = ß1ln(x) + ß2(ln(x))^2

is it:

f(x)' = ß1/x + 2*ß2ln(x)

???

Thanks!

You forgot the chain rule.

The derivative is:

b1*1/x + b2*2*ln(x)/x.

 

[mrkun]

Originally posted by: BigJ
I'm actually glad when people post questions like this. It shows they're actually trying to work on a problem and figure out how you arrive at the solution rather then plugging it into a Ti-89, Maple, or Mathematica to get a solution.

How do these people take tests then?

 

[Jeff7]

Originally posted by: BigPoppa

I did that in high school. Then I got to college and almost got owned when I couldn't do simple stuff like the chain rule. Now my single variable (have yet to reach calc3) integral and derivative skills are excellent thanks to only using a simple 2 line TI scientific calulator.

My calculator wasn't even capable of doing calculus. It was some Casio thing. Or maybe it was, I just never tried it.

I had calculus in high school. I took it again in college because it didn't make a damn bit of sense to me in school. I didn't know the point, I didn't get what was being done to the variables, and really, it was all just an unpleasant blur. Things were being written on the board that were quite meaningless to me.
Now it's only a little bit clearer.

 

[Minjin]

I use HP calculators and I've honestly never figured out how to do calculus on them so I'm forced to do it on paper...

 

[White Widow]

Just so y'all know, I am taking a class on regression, and we have started interpreting regressions when we use log transformed variables. I was trying to basically "visualize" what is going on with the curve as x changes. It's easy to "see" what B1-2*B2*x looks like and why it behaves the way it does, but thinking about what it means to have diminishing marginal returns to "ln(x)" is something else entirely. I realize that you can treat "ln(x)" as just another "x" , use the plain-jane quadratic story (if the data fits) and in the end when it spits out a logged value, turn that back into something meaningful. Nevertheless, I was trying to see what was actually going on here. Thanks for the help. Now if I could only "see" how we get the determinant of a matrix...