The dot product (denoted with *) of n-length vectors a and b defined as (a1,a2,...,an)*(b1,b2,...,bn) = a1b1+a2b2+...+anbn. It is the vector equivalent of scalar multiplication; its result happens to be equal to ||a||*||b||cos(t) where t is the angle between the vectors. ||v|| denotes the magnitude of v; note that ||v|| = sqrt(v*v) much as how |x| = sqrt(x*x).