Читать книгу Mathematics for Enzyme Reaction Kinetics and Reactor Performance - F. Xavier Malcata - Страница 39

The simpler operation involving vectors is addition; to be applied to u and v, the point of origin of v must be made coincident with the point of termination of u . The vector sum, u + v, is thus the vector with the same point of origin of u and the same point of termination of v, as apparent in Fig. 3.1a. Therefore, one finds in general

(3.17)

with the equal sign holding when u and v are collinear with the same orientation; coupled with

(3.18)

with the equal sign holding again when u and v are collinear and point in the same direction. Here ∠ u, v and ∠ u, u + v denote the angles formed by vectors u and v, and by vectors u and u + v, respectively. Since such coordinates are simply the normal projection of the vector at stake onto the corresponding Cartesian axes, addition of two vectors corresponds to merely adding the homologous coordinates, i.e.

(3.19)

based on Eqs. (3.1) and (3.2); both these statements are apparent from inspection of Fig. 3.1a.

Figure 3.1 Graphical representation of (a) addition of two vectors, u and v, and (b) multiplication of scalar α by vector u .

Addition of vectors is commutative – since, according to Eq. (3.19),

(3.20)

this is equivalent to

(3.21)

as per the commutative property of addition of scalars – so

(3.22)

following combination of Eqs. (3.19) and (3.21).

Given a third vector w – defined as

(3.23)

one may recall Eqs. (3.1), (3.2), and (3.19) to write

(3.24)

because of the commutative property of vector addition as per Eq. (3.22), one can rewrite Eq. (3.24) as

(3.25)

whereas Eq. (3.19) leads to

(3.26)

with the aid of Eqs. (3.1), (3.2), and (3.23). Algebraic rearrangement of Eq. (3.26) – at the expense again of Eq. (3.19), produces

(3.27)

which leads directly to

(3.28)

due to Eq. (3.22); one finally attains

(3.29)

in view again of Eqs. (3.19) and (3.23) – so addition of vectors is associative.