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## Homework Statement

Prove that if v(t) is any vector that depends on time, then v'(t) is orthogonal to v(t).

Hint given: Consider the derivative of v^2.

## The Attempt at a Solution

V'^2 = d/dt (v * v)

= v d/dt + v d/dt

= d/dt (v+v)

= 2v d/dt

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