||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) = 9.4868I 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