How to prove that this function is primitive recursive?

How do you show/derive/prove this vector-valued function identity?

  • R(t) is a vector-valued function. Please show that d/dt (||R(t)||) = [R(t) · R'(t)] / ||R(t)|| Note: R is supposed to have an arrow above it and || || means absolute value. * I cannot answer this exercise . Please help me. I've tried using implicit differentiation and basic identities of dot products.

  • Answer:

    Hmm, it looks like the scalar projection formula scalar projection of vector b on vector a = a.b/|a| see your equation with this approach scalar projection of R' on R = R.R'/|R| is d/dt( |R(t)| ) = scalar projection of R' on R?

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