# Vector Magnitude Equation

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Hey guys, I'm reading through 3D Math Primer for Graphics and Game Development, and on page 50 (for those that have the book handy), it gives the equation for calculating the magnitude of a vector. It works great and I understand it properly, bar one thing. Here's the example from the book:
||v|| = sqrt(vx² + vy² + vz²) (for a 3D vector v)

Example:

|| [5, -4, 7] || = sqrt(5² + (-4²) + 7²)
= sqrt(25, 16, 49)
= sqrt(90)
= 3sqrt(10)
= 9.4868

I understand it up to the point of sqrt(90) (obviously this works and gives the same result), but how does the author get 3sqrt(10) from all of that? Thanks in advance, -hellz

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sqrt(90) == sqrt(9*10) == sqrt(9) * sqrt(10) == 3 * sqrt(10)

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Ahhh, that makes sense. Thanks very much, and do you get the award for the fastest reply, or what. [grin]

-hellz