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February 27th, 2015, 02:31 PM  #1 
Newbie Joined: Feb 2015 From: Lithuania Posts: 3 Thanks: 0  How to calculate a curvature of the cubic function.
Hi, I need some help. I have a cubic function: f(x)=ax^3+bx^2+cx+d and I need to say (to prove) which formula is better to use to calculate a curvature: k=1/R or k=f''(x)/(1+(f'(x)^2)^3/2. The answer have to be proved. Maybe there is no difference and they both give me the same result, but I have to prove it. (Here is the link, where are the both formulas: Curvature  Wikipedia, the free encyclopedia) 
February 28th, 2015, 12:38 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 18,408 Thanks: 1459 
There isn't an easy way to calculate R, so use the second formula. The numerator should be f''(x).

March 2nd, 2015, 11:31 AM  #3 
Newbie Joined: Feb 2015 From: Lithuania Posts: 3 Thanks: 0 
But I have to explain, why the second formula it's better than first one. Maybe it's more accurate or something else. I got the task, that, based on the theory I have to explain and prove which formula it's better to use.


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calculate, cubic, curvature, function, prove 
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