Perpendicular
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Two lines and
are said to be perpendicular if they intersect in right angles. We denote this relationship by
. In the Cartesian coordinate system, a line with slope
is perpendicular to every line with slope
and no others.
One can also discuss perpendicularity of other objects. If a line intersects a plane
at a point
, we say that
if and only if for every line
in
passing through
,
.
If a plane intersects another plane
in a line
, we say that
if and only if:
for line
and
passing through
,
and
implies
.