How Do You Calculate Time in the Brachistochrone Problem?

hriby
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I hope that you've heard about Brachistochrone problem: http://mathworld.wolfram.com/BrachistochroneProblem.html
Given two points, I can find (calculate) the courve, on which the ball needs minimum time to travel from point 1 to point 2.
I get the equation for the courve, which is cycloid, in parametric form, let say:
<br /> x(\theta)&amp;=&amp;C\left(\theta-\sin{\theta}\right),<br />

<br /> y(\theta)&amp;=&amp;-C\left(1-\cos{\theta}\right).<br />

Now I also need to calculate the time needed...
How could I calculate it out of formula below using the equation for the courve/cycloid in parametric form?
t_{12}=\int_{T_1}^{T_2} \frac{\sqrt{1+{y&#039;}^2}}{\sqrt{2g\,y}}dx, \quad y&#039;=\frac{dy}{dx}
Thanks for your answers!
Hriby
 
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how 'bout:

dy/dx = (dy/d_theta)/(dx/d_theta)
 
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