Linear algebra
Linear algebra grew with ideas noted in the complex plane. For instance, two numbers "w" and "z" in formula_3 have a difference "w" – "z", and the line segments formula_4 and formula_5 are of the same length and direction. The segments are equipollent. The four-dimensional system formula_6 of quaternions was started in 1843. The term "vector" was introduced as "v" = "x" i + "y" j + "z" k representing a point in space. The quaternion difference "p" – "q" also produces a segment equipollent to formula_7