Simple calculus problem, and how to fix my TI-89

[Pirian]

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[Cleverness]

Are you remembering to apply the Product rule for differentiating the xy^3 and yx^3?

Edit: And the x^2 y^2 also. I'm sorta occupied so I can't work it out but that's a common mistake I see people make when doing differentiation with multiple terms like this.

[Pirian]

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[aurik]

might help if you transcribe the calculator input/output instead of providing an unreadable pic.

[Avelain]

^ what aurik said, the picture is pretty unreadable and chances are you're putting it into your calculator improperly

[Cleverness]

Like you are missing a multiplication sign on x * y^3 near the end, not sure how fickle the TI-89 is since I didnt use it really but that could mess with your answer too.

[Ferion]

Are you remembering to apply the Product rule for differentiating the xy^3 and yx^3?

Edit: And the x^2 y^2 also. I'm sorta occupied so I can't work it out but that's a common mistake I see people make when doing differentiation with multiple terms like this.

You don't need the product rule for anything in the equation he has listed, you're taking a partial derivative so "x" is treated as a constant.

[Blubbartron]

Like you are missing a multiplication sign on x * y^3 near the end, not sure how fickle the TI-89 is since I didnt use it really but that could mess with your answer too.

Given that this is the term that's lacking the partial derivative in the answer given, I'll wager a guess that this man is correct.

[Pirian]

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[Cleverness]

You don't need the product rule for anything in the equation he has listed, you're taking a partial derivative so "x" is treated as a constant.

Yea I realized that after you posted it, haven't had to tutor calculus in forever so confused it with regular derivative.

Definitely the calculator thing though as I guessed, 1 sign fucks it all up lol. Hence why my professor never let us really use it.

[Elesirdur]

http://www.wolframalpha.com/ will do most of the work your TI-89 can, entirely for free through a web browser or $0.99 for a dedicated Android/iOS app.

Calculators and stuff like WolframAlpha are great for checking your work, but relying too much on them can really f you over if you don't really understand the underlying principals - particularly in calculus. Glad to see you're on this track.

If you're going to be doing math, hard sciences, or Economics it might be worth trying out Mathematica or MatLab for mathematical software. Your school's comp lab may have copies installed, and they're not too hard to pirate.

[Pirian]

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[Elesirdur]

Ah cool, I'm in Econ to, though doing a BSc program that's pretty math/econometrics heavy. My uni has a reputation as a place for econometricians at the graduate level, so there's a pretty heavy focus on the mathematical principals in the coursework at the 3rd/4th year level. If you're just doing an applied econometrics course where most of the heavy lifting is being done by a statistical software package (ie. EViews), you should only have to worry about taking partial derivatives to examine the extimated change in your dependent variable when you change one independent/exogenous variable, ceteris paribus.

If you do some more mathematics for economists courses you'll be introduced to matrix algebra and multivariate calculus, if you haven't seen them already. When it all boils down, math in econ is really about three things: where to two lines cross, where two curves are tangent, and where they just touch lol

If you've got any Econ-related questions feel free to shoot me a PM. I'm working in the help centre this year so I can always use the practice

[Ferion]

Ah cool, I'm in Econ to, though doing a BSc program that's pretty math/econometrics heavy. My uni has a reputation as a place for econometricians at the graduate level, so there's a pretty heavy focus on the mathematical principals in the coursework at the 3rd/4th year level. If you're just doing an applied econometrics course where most of the heavy lifting is being done by a statistical software package (ie. EViews), you should only have to worry about taking partial derivatives to examine the extimated change in your dependent variable when you change one independent/exogenous variable, ceteris paribus.

If you do some more mathematics for economists courses you'll be introduced to matrix algebra and multivariate calculus, if you haven't seen them already. When it all boils down, math in econ is really about three things: where to two lines cross, where two curves are tangent, and where they just touch lol

If you've got any Econ-related questions feel free to shoot me a PM. I'm working in the help centre this year so I can always use the practice

Your Econ classes introduced matrix algebra and multivariate calc? Even my advanced Econometrics professor refused to introduce linear algebra into his lectures unless you went to him after class because our school didn't require econ majors to know it. In my financial economics class on the first day the professor put up a slide of how to compute the probability of a continuous random variable, at least a third of the class dropped the course by the next time we met.

[Elesirdur]

My school, the University of Victoria, is one of the few that offers a BSc program in Economics which requires you to take a few extra econ math and econometrics courses compared to the regular BA stream. Most BA students don't really take much in the way of math/econometrics so their upper-year coursework is mostly theory courses. If they choose to go to grad school, they'll likely get their asses kicked when they introduce the grad econ math and econometrics (calculating multi-variate OLS regressions using matrices, for example). With our BSc program, you get a lot of that in your undergrad and are much more prepared to tackle the higher-level empirical work required in MA coursework.

If you're still doing an Econ degree and are seriously thinking of doing a Masters, or even getting your CFA, take an econometrics course (not just an applied one, but one that covers the stats theory too) and some kind of math course that covers matrix algebra and multi-variate calculus - they seem to be used very extensively in econometrics and even with econometric/mathematical software packages like EViews, MAPLE, MatLab, etc.

[Ferion]

My school, the University of Victoria, is one of the few that offers a BSc program in Economics which requires you to take a few extra econ math and econometrics courses compared to the regular BA stream. Most BA students don't really take much in the way of math/econometrics so their upper-year coursework is mostly theory courses. If they choose to go to grad school, they'll likely get their asses kicked when they introduce the grad econ math and econometrics (calculating multi-variate OLS regressions using matrices, for example). With our BSc program, you get a lot of that in your undergrad and are much more prepared to tackle the higher-level empirical work required in MA coursework.

If you're still doing an Econ degree and are seriously thinking of doing a Masters, or even getting your CFA, take an econometrics course (not just an applied one, but one that covers the stats theory too) and some kind of math course that covers matrix algebra and multi-variate calculus - they seem to be used very extensively in econometrics and even with econometric/mathematical software packages like EViews, MAPLE, MatLab, etc.

Yeah I graduated already. I was a dual econ/math major. Was considering going to graduate school, but I got really burnt out on undergraduate research so I'm just working in business while I figure out what I want to do. If you haven't already I would suggest that you look into SAS as it seems to be the most applicable statistical package once you graduate.