addition
and 
be directed line segments that represent a and b, with the same initial point O. The sum of 
and 
is the directed line segment 
, where 
is a parallelogram, and the sum a + b is defined to be the vector c represented by 
. Alternatively, the sum of vectors a and b can be defined by representing a by a directed line segment 
and b by 
where the final point of the first directed line segment is the initial point of the second. Then a + b is the vector represented by 
. Addition of vectors has the following properties, which hold for all a, b, and c:
Parallelogram law for addition
Triangle law for addition
Addition of coordinate vectors in n-dimensional space is done componentwise. So if a = (a1, a2,…,an) and b = (b1, b2,…,bn), then a + b = (a1 + b1, a2 + b2,…, an + bn).
- decimal representation
- decision analysis
- decision nodes
- decision problem
- decision theory
- decision tree
- decision variables
- deci‐
- declination
- decompose
- decomposition
- decreasing function
- decreasing sequence
- Dedekind cut
- Dedekind, (Julius Wilhelm) Richard
- deduction
- deficient number
- definite integral
- deformation
- degenerate
- degenerate conic
- degenerate quadric
- degree
- degree
- degree