Supergrunch Posted February 14, 2006 Share Posted February 14, 2006 Basically, the question I have to answer is as follows: f '(x)=e^((-x)^2) find f '(3x). I'm aware that it has something to do with setting f(3x) to f(y), and then working out a calculus formula using the chain rule and those limit of delta y over delta x fractions, but I'm don't really know exactly how to proceed. Obviously you can't simply find f(x), as f '(x) can't be integrated, so there must be some side route to do with what I said earlier. Any help? Link to comment Share on other sites More sharing options...
Mr_Odwin Posted February 14, 2006 Share Posted February 14, 2006 Have you written it correctly? You have f '(x) and need to show what f '(3x) is? That's really easy. Eg. If f '(x)=5x^2+12x+1 then f '(4x)=5*(4x)^2+12*(4x)+1. Link to comment Share on other sites More sharing options...
Wesley Posted February 14, 2006 Share Posted February 14, 2006 What the fuck? I stopped maths at GCSE and I was in top set, either this is harder stuff or I've just lost all math skill. Link to comment Share on other sites More sharing options...
Domo Kun Posted February 14, 2006 Share Posted February 14, 2006 For the love of God! MAKE IT STOP! IT HURTS IT HURTS! Link to comment Share on other sites More sharing options...
Supergrunch Posted February 14, 2006 Author Share Posted February 14, 2006 Have you written it correctly?You have f '(x) and need to show what f '(3x) is? That's really easy. Eg. If f '(x)=5x^2+12x+1 then f '(4x)=5*(4x)^2+12*(4x)+1. Yes, I did write it wrong... I need to differentiate f(3x) with respect to x. And given that you can't find f(x), it's a pretty evil question. Link to comment Share on other sites More sharing options...
Mr_Odwin Posted February 14, 2006 Share Posted February 14, 2006 What does the question say exactly? Link to comment Share on other sites More sharing options...
Supergrunch Posted February 14, 2006 Author Share Posted February 14, 2006 Fine: "The function f(x) has the property f '(x) = e^(-x^2) Differentiate f(x^3) with respect to x." Actually I had it very wrong... sorry about that. Link to comment Share on other sites More sharing options...
Andrew Posted February 14, 2006 Share Posted February 14, 2006 What the fuck? I stopped maths at GCSE and I was in top set, either this is harder stuff or I've just lost all math skill. I'm doing A level maths, and I'm not even sure if I could answer Supergrunch's question. Link to comment Share on other sites More sharing options...
Mr_Odwin Posted February 14, 2006 Share Posted February 14, 2006 Use the chain rule. If dy/dx = dy/du * du/dx (Don't know the notation you're used to.) then the question gives you dy/du, and du/dx is simple differentiating of x^3. Link to comment Share on other sites More sharing options...
The Peeps Posted February 14, 2006 Share Posted February 14, 2006 Yes.. Mr_Odwin is correct... *shifty eyes* Link to comment Share on other sites More sharing options...
Supergrunch Posted February 14, 2006 Author Share Posted February 14, 2006 So it would be: 3x^2*e^(-x^2)? Anyway, thats the right notation (for the chain rule). Link to comment Share on other sites More sharing options...
Mr_Odwin Posted February 14, 2006 Share Posted February 14, 2006 Edit: I get a different power for the x in the exponential, but otherwise agree. Original post: Further hint before I'm off to bed: u=x^3 and you know what f '(u) is. *goes to bed* Link to comment Share on other sites More sharing options...
Supergrunch Posted February 14, 2006 Author Share Posted February 14, 2006 Actually I now have: 3x^2*e^(-x^6) Which I think is right so many thanks... but being in bed, you won't reply. :-p Link to comment Share on other sites More sharing options...
Mr_Odwin Posted February 15, 2006 Share Posted February 15, 2006 Actually I now have: 3x^2*e^(-x^6) Which I think is right so many thanks... but being in bed, you won't reply. :-p That's what I got. Link to comment Share on other sites More sharing options...
Shorty Posted February 15, 2006 Share Posted February 15, 2006 I bet you guys are so glad you learned all this stuff. Now, when you're at the supermarket and there's a mistake at the check-out, these formulae will save the day. Link to comment Share on other sites More sharing options...
Dark Wolf Posted February 15, 2006 Share Posted February 15, 2006 Quite a lot of maths is pretty pointless. I mean, when are you ever gonna use surds in real life? WHAT IS THE POINT! Link to comment Share on other sites More sharing options...
Mr_Odwin Posted February 15, 2006 Share Posted February 15, 2006 This sort of maths is the sort of maths used in engineering, financial prediction, ecology models, epidemic models, population dynamics ... So ... er ... Edit: Surds make notation easier and clearer. Link to comment Share on other sites More sharing options...
AshMat Posted February 15, 2006 Share Posted February 15, 2006 Quite a lot of maths is pretty pointless. I mean, when are you ever gonna use surds in real life? WHAT IS THE POINT! This is what i think every crappy maths lesson, my parent won't let me move down a set . Give me 2 instances where i ama ctually going to use pythagoras please. And where i'm actually going to need to work out an anglew, when i'll have a protractor. What level maths is this anyway? Link to comment Share on other sites More sharing options...
masaki86 Posted February 15, 2006 Share Posted February 15, 2006 I did a level maths; I got a D......I always like Pure and statistics, but Mechanics blew the big one.... This is what i think every crappy maths lesson, my parent won't let me move down a set .Give me 2 instances where i ama ctually going to use pythagoras please. And where i'm actually going to need to work out an anglew, when i'll have a protractor. What level maths is this anyway? Numbers are important; if you don't get a decent maths GCSE you may struggle to get decent jobs. A lot want at least a C at GCSE Link to comment Share on other sites More sharing options...
Bogbas Posted February 15, 2006 Share Posted February 15, 2006 Well probably you won't be using pythagoras in most workplaces. But having a good degree in maths helps you in getting into universities, and finding jobs. And this thread remids me that I really should start reading for my entrance exams... I know that I should be able calculate the stuff that's on this thread. I just don't remember how it's done. Link to comment Share on other sites More sharing options...
Supergrunch Posted February 15, 2006 Author Share Posted February 15, 2006 This sort of maths is the sort of maths used in engineering, financial prediction, ecology models, epidemic models, population dynamics ...So ... er ... Edit: Surds make notation easier and clearer. Actually, if we ask our maths teacher if what we're doing is any use, he says "God no... What do you take me for?". Anyway, what has this question got to do with surds? And in answer to retro-lover, this maths is A2 level. Link to comment Share on other sites More sharing options...
Daniel Posted February 15, 2006 Share Posted February 15, 2006 i think that question was worded very strangly, took me some time to decipher it and im currently doing a degree in maths :P Link to comment Share on other sites More sharing options...
Supergrunch Posted February 15, 2006 Author Share Posted February 15, 2006 i think that question was worded very strangly, took me some time to decipher it and im currently doing a degree in maths :P Yeah my teacher said that he thought about 2% of the people who took the exam got it right... it makes sense, it's just a bit confusing. Link to comment Share on other sites More sharing options...
Mr_Odwin Posted February 15, 2006 Share Posted February 15, 2006 I don't think it's confusing. Link to comment Share on other sites More sharing options...
Daniel Posted February 15, 2006 Share Posted February 15, 2006 i dont think its confusing anymore lol but took me a min or 3 to figure out how to go about it Link to comment Share on other sites More sharing options...
Recommended Posts