Difference between revisions of "Vector"
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== Addition of Vectors == | == Addition of Vectors == | ||
For vectors <math>\vec{v}</math> and <math>\vec{w}</math>, with angle <math>\theta</math> formed by them, <math>(\vec{v}+\vec{w})^2=||\vec{v}||^2+||\vec{w}||^2-2||\vec{v}||||\vec{w}||\cos\theta</math>. | For vectors <math>\vec{v}</math> and <math>\vec{w}</math>, with angle <math>\theta</math> formed by them, <math>(\vec{v}+\vec{w})^2=||\vec{v}||^2+||\vec{w}||^2-2||\vec{v}||||\vec{w}||\cos\theta</math>. | ||
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From this it is simple to derive that for a real number <math>c</math>, <math>c\vec{v}</math> is the vector <math>\vec{v}</math> with magnitude multiplied by <math>c</math>. Negative <math>c</math> corresponds to opposite directions. | From this it is simple to derive that for a real number <math>c</math>, <math>c\vec{v}</math> is the vector <math>\vec{v}</math> with magnitude multiplied by <math>c</math>. Negative <math>c</math> corresponds to opposite directions. |
Revision as of 13:05, 29 November 2007
A vector is a magnitude with a direction. A vector is usually graphically represented as an arrow. Vectors can be uniquely described in many ways. The two most common is (for 2-dimensional vectors) by describing it with its length (or magnitude) and the angle it makes with some fixed line (usually the x-axis) or by describing it as an arrow beginning at the origin and ending at the pint . An -dimensional vector can be described in this coordinate form as an ordered -tuple of numbers within angle brackets or parentheses, . The set of vectors over a field is called a vector space.
Contents
[hide]Description
Every vector has a starting point and an endpoint . Since the only thing that distinguishes one vector from another is its magnitude,i.e. length, and direction, vectors can be freely translated about a plane without changing them. Hence, it is convenient to consider a vector as originating from the origin. This way, two vectors can be compared only by looking at their endpoints. This is why we only require values for an dimensional vector written in the form . The magnitude of a vector, denoted , is found simply by using the distance formula.
Addition of Vectors
For vectors and , with angle formed by them, .
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From this it is simple to derive that for a real number , is the vector with magnitude multiplied by . Negative corresponds to opposite directions.
Properties of Vectors
Since a vector space is defined over a field , it is logically inherent that vectors have the same properties as those elements in a field.
For any vectors , , , and real numbers ,
- (Commutative in +)
- (Associative in +)
- There exists the zero vector such that (Additive identity)
- For each , there is a vector such that (Additive inverse)
- (Unit scalar identity)
- (Associative in scalar)
- (Distributive on vectors)
- (Distributive on scalars)
Vector Operations
Dot (Scalar) Product Consider two vectors and in . The dot product is defined as .
Cross (Vector) Product
The cross product between two vectors and in is defined as the vector whose length is equal to the area of the parallelogram spanned by and and whose direction is in accordance with the right-hand rule.
Triple Scalar product The triple scalar product of three vectors is defined as . Geometrically, the triple scalar product gives the signed area of the parallelpiped determined by and . It follows that
It can also be shown that
Triple Vector Product
See Also
Related threads from AoPS forum
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