Re: Deriviation d/dt(x(t))

*To*: mathgroup at smc.vnet.net*Subject*: [mg27442] Re: [mg27407] Deriviation d/dt(x(t))*From*: BobHanlon at aol.com*Date*: Sun, 25 Feb 2001 20:55:46 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Dt[x^2 + y^2 == r^2, t, Constants -> {r}] 2*x*Dt[x, t, Constants -> {r}] + 2*y*Dt[y, t, Constants -> {r}] == 0 or Dt[x^2 + y^2 == r^2, t] /. Dt[r, t] -> 0 2*x*Dt[x, t] + 2*y*Dt[y, t] == 0 or D[x[t]^2 + y[t]^2 == r^2, t] 2*x[t]*Derivative[1][x][t] + 2*y[t]*Derivative[1][y][t] == 0 Bob Hanlon In a message dated 2001/2/25 1:14:25 AM, maier1 at sbox.tu-graz.ac.at writes: >I have a problem, having a definition of a circle: x^2+y^2=r^2 >Where x and y are functions of the time: x(t), y(t) and r ist a constant. > >Now I want to deriviate the equation to get the velocity vector. >It should be : 2 x dx/dt +2 y dy/dt = 0 > >Can anyone tell me how to do? >