- #1
seeingstars63
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Homework Statement
Prove that the shortest path between two points in three dimensions is a straight line. Write the path in the parametric form:
x=x(u) y=y(u) z=z(u)
and then use the 3 Euler-Lagrange equations corresponding to ∂f/∂x=(d/du)∂f/∂y'.
Homework Equations
Stated them above:]
The Attempt at a Solution
I found all of the answers in relation to the Euler-Lagrange equations, but I am not sure where to go from there. For each coordinate, ∂f/∂x,∂f/∂y,∂f/∂z, they all equal 0 so that means that d/du(∂f/∂x,y,z) are all also zero. As a result, I get constants for each and hence don't know how to implement these constants into a straight line equation.
The constants are :
∂L/∂x'=x'(u)/(x'(u)^2 +y'(u)^2 +z'(u)^2)^(1/2)=C_1
∂L/∂y'=y'(u)/(x'(u)^2 +y'(u)^2 +z'(u)^2)^(1/2)=C_2
∂L/∂z'=z'(u)/(x'(u)^2 +y'(u)^2 +z'(u)^2)^(1/2)=C_3