# Operations involving vectors

Vector algebra involves several different types of values; in this course, we study scalars, points, and vectors. We can try to add these, subtract them, and multiply them in various ways. Sometimes these operations make sense, and sometimes they don't, with results as in this table:
Scalar:  Scalar   Scalar   Scalar Vector
Point:  Point  Vector Point
Vector:  Point Vector  Vector  Vector Depends
There are various ways to multiply two vectors, with results as in this table:
NameSymbolResult Order matters?Depends on lengths? Depends on the right-hand rule?
Dot product ScalarNo YesNo
Cross product× Scalar in 2D,
vector in 3D
YesYes Yes
There are actually other ways to multiply vectors besides these, but we don't cover them in this course.

The cross product in 2 dimensions is not in the textbook; here is the formula for it (using the right-hand rule):

a, b⟩ × ⟨c, d⟩ = ad − bc.
Geometrically,
u × v = |u| |v| sin∠(u, v),
where ∠(u, v), the measure of the angle from u to v, is positive if this angle is counterclockwise (using the right-hand rule) and negative if it's clockwise.
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