- #1

- 91

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δ(dq/dt) = d(δq)/dt

Where q is some coordinate, and δf is the first variation in f. In general, this can be seen more broadly, given a scalar field ψ

δ(∂ψ/∂x) = ∂(δψ)/∂x

Where x is any independant variable (i.e. x,y,z,t or any other coordinate system)

How are these equalities justified?