IMPORTANT THEOREMS ON QUADRILATERALS
THEOREM 1: If a parallelogram has one right
angle, then it has four right angles
and the parallelogram is a
rectangle.
THEOREM 2: The diagonals of a rectangle are
congruent.
THEOREM 3: The diagonals of a rhombus are
perpendicular.
THEOREM 4: Each diagonal of a rhombus bisects
opposite angles.
THEOREM 5: The segment that joins the
midpoints of two sides of a triangle
is parallel to the third side and half
as long. (Midline Theorem)
THEOREM 6:The median of a trapezoid is
parallel to each base and its length
is one-half the sum of the lengths
of the bases.
THEOREM 7: The base angles of an isosceles
trapezoid are congruent.
THEOREM 8: Opposite angles of an isosceles
trapezoid are supplementary.
THEOREM 9: The diagonals of an isosceles
trapezoid are congruent.
THEOREM 10: The diagonals of a kite are
perpendicular to each other