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I have a velocity vector on $X$, $Y$ and $Z$ axes. The values are represented as M/S (meters per second).

What algorithm should I use to convert this vector into a general MPH (miles per hour) value that takes into account all axes of the vector?

This may (or may not) be a very simple question. But I am far from being a genius at math! So apologies.

Thanks very much.

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Multiply each coordinate by 2.23693629. In general, to convert units of a vector, you just convert units of each coordinate. This works because scalar multiplication by positive constants preserves direction, and because lengths of vectors and scalar multiplication are related by $\|c v\|=|c|\|v\|$. Scalar multiplication in this case just means multiplying each coordinate by the conversion factor.

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    @Nathan: You don't need the Abs() around the squares, as the square of a real number is necessarily non-negative.2010-11-06