Draw a convex quadrilateral ABCD, where the diagonals intersect
at point M. Prove: If ABCD is a parallelogram, then M is the
midpoint of each diagonal.
Perpbisogram Definition: A perpbisogram of a
quadrilateral is a polygon formed by the perpendicular bisectors of
the sides of the quadrilateral.
Prove the following theorem
The angles of a trapezoid are congruent to the angles of its
perpbisogram.
(SHOW DIAGRAM)
Prove the following theorem:
In a Pasch geometry, a quadrilateral is a convex quadrilateral
if and only if the vertex of each angle is contained in the
interior of the opposite angle.
In hyperbolic geometry, suppose ABCD is a quadrilateral with
right angles at C and D such that AD = BC. Show that AB > CD.
Hint: Use Proposition 24 of Euclid.
Let E be a projective conic through the quadrilateral ABCD, and
let the tangents to E at A and C meet at P on the Line BD. Show
that the tangents to E at B and D meet at a Point Q on AC.
Hint: Consider poles and polars.
Write up a formal proof that the angle bisectors of a triangle
are concurrent, and that the point of concurrency (the incenter) is
equidistant from all three sides.
Prove that if two of the opposite sides of a quadrilateral are
respectively the greatest and the least sides of the quadrilateral,
then the angles adjacent to the least are greater than their
opposite angles.