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MillerGenuine
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Homework Statement



Find the length of the curve y=x^3 using P(1,1) as the starting point

Homework Equations




<br /> f(x) = \int_{a}^{x} {\sqrt 1 + {f&#039;(t)}^2}<br />



The Attempt at a Solution



So far all I've done is found my y' and plugged it in, giving me 1+9t^4 inside the square root...now from here I am not sure whate technique to use to do the integral.
 
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looks like a classic trig sub integral
 
lanedance said:
looks like a classic trig sub integral

If only. Checking Wolfram-Alpha, you'll require the Elliptic Integral of the First kind to solve this. A simple trig sub works with functions of the form sqrt(a^2 + (bx)^2), but not sqrt(a^4 + (bx)^4).
 
fair bump, play on
 
MillerGenuine said:

Homework Statement



Find the length of the curve y=x^3 using P(1,1) as the starting point

Homework Equations




<br /> f(x) = \int_{a}^{x} {\sqrt 1 + {f&#039;(t)}^2}<br />



The Attempt at a Solution



So far all I've done is found my y' and plugged it in, giving me 1+9t^4 inside the square root...now from here I am not sure whate technique to use to do the integral.
Is there an end point given? If so, you run into the problem pointed out by Char Limit. If not, are you just supposed to find an expression that represents the length from (1, 1) to an arbitrary point (x, x3)?

If it's the latter, here's a function that gives the length along the curve. Although difficult to integrate analytically, it can be approximated by a number of numerical integration techniques.
L(x) = \int_1^x \sqrt{1 + 9t^4}dt
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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