Where did the bracket notation for vectors come from and is using parentheses to represent vectors valid? In class I learned that a vector can be represented using &lt;>, a column vector, and unit vector notation. However, one of the old math books that I study from notes that a vector in unit vector form can be represented with parantheses:

"Let $n$ be a positive integer. An ordered n-tuple of real numbers $$(a_1,a_2,...,a_n)$$ is called a vector in n-space. The set of all such vectors, $a_i$ real, under operations to be explained, is called Euclidean n-space, $E^n$."

This book is Calculus And Analytic Geometry Fourth Edition (1968) by George B. Thomas, Jr.

Is this parentheses notation still used? If so, is it uncommon?
This is the standard notation in quantum mechanics. It's great, because it allows to incorporate operators as well. 

Copied from Wikipedia


  Bra–ket notation was effectively established in 1939 by Paul
  Dirac1[2] and is thus also known as the Dirac notation.
This is the standard notation in quantum mechanics. It's great, because it allows to incorporate operators as well. 

Copied from Wikipedia


  Bra–ket notation was effectively established in 1939 by Paul
  Dirac1[2] and is thus also known as the Dirac notation.