Vector

A quantity with a magnitude and a direction. Vectors are added like arrows, end to end, and the sum (for two) is the vector from the tail of the first vector to the tip of the second.

There are a number of different representations. Given the vector A it is normal to print it in bold or it can be expressed as follows:

are unit vectors

If x₁=0 it is customary to omit it, eg

See also: Cauchy-Schwarz Inequality, Dot Product, Magnitude, Scalar.