A Level Maths Notes: FP4 – Linear Independence and Volumes of Parallelpipeds
If the vectors
and
are
joined by a third vector
to
form a solid shape, then the volume of the solid is the area of the
base (which we may consider to be the area of the parallelpiped
formed by
and
)
multiplied by the height.
is
perpendicular to both
and
so
is in the direction of the vertical height. By taking the dot product
of
with
and
dividing by
we
obtain the component of
perpendicular
to
This
is the height of the parallelpiped. Multiplying by
gives
the volume: This is illustrated below.
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If the vectors
are
in the same plane, then they are linearly dependent, since three
vectors in a two dimensional space are linearly dependent. They all
lie in the same plane and the height of the parallelpiped is zero. If
a matrix is formed with the columns or rows consisting of the three
vectors, the determinant of this matrix will be zero since the
vectors are linearly dependent.