Editing Mohr–Mascheroni theorem (section)

==== Reflecting a point across a line ====
[[File:PointReflection.png|thumb|Point symmetry]]
* Given a line segment {{math|{{overline|''AB''}}}} and a point {{mvar|C}} not on the line determined by that segment,  construct the image of {{mvar|C}} upon reflection across this line.
# Construct two circles: one centered at {{mvar|A}} and one centered at {{mvar|B}}, both passing through {{mvar|C}}.
# {{mvar|D}}, the other point of intersection of the two circles, is the reflection of {{mvar|C}} across the line {{math|{{overline|''AB''}}}}.
#* If {{math|1=''C'' = ''D''}} (that is, there is a unique point of intersection of the two circles), then {{mvar|C}} is its own reflection and lies on the line {{math|{{overline|''AB''}}}} (contrary to the assumption), and the two circles are internally tangential.

{{clear}}