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# Find radius of curvature watch

1. Find radius of curvature of y=k.arctan(x/k)

I keep on getting p=25kroot(41)/80, which is wrong...

Anyone out there?
2. I get a fairly complex result for rho. What's the value of x for that result of yours?

I have p=[1+(1+x^2/k^2)^2]^(3/2).k^2(1+x^2/k^2)^2/(-2x)
3. .25? i'm ok now. I only checked back to say I think I'm ok... but you had already written your thing down. cheers anyway man. I forgot that you raise the top bit to 3/2 and not 1/2. it's that time of the day when I should be asleep... lol
4. (Original post by Yannis)
Find radius of curvature of y=k.arctan(x/k)

I keep on getting p=25kroot(41)/80, which is wrong...

Anyone out there?
p = [(1+(dy/dx)²)^3/2]/[d²y/dx²]

dy/dx = k/(k²+x²)

d²y/dx² = -2xk/(k²+x²)²

p = [(1+k²/(k²+x²)²)^3/2]/[-2kx/(k²+x²)]

= [[(k²+x²)²+k²]/(k²+x²)²]^3/2].(x²+k²)/(-2kx)

dot dot dot

it's pretty tedius algebra from there
5. cheers man... I suppose you were working on it before I got to post my last one. Thanks a bunch anyway. At least I know there are some people around if I need help. I'm pretty sure I've sorted it now. I just forgot the power of [1 + (dy/dx)^2] bit. too late.

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