Tests for Parallelograms

1
Lesson 6-2

• Tests for Parallelograms

2
Proving Quadrilaterals as Parallelograms
Theorem 1
If both pairs of opposite sides of a
quadrilateral are congruent, then the
quadrilateral is a parallelogram .
H
G
Theorem 2
E
F
If one pair of opposite sides of a quadrilateral
are both congruent and parallel, then the
quadrilateral is a parallelogram .
3
Theorem
Theorem 3
If both pairs of opposite angles of a
quadrilateral are congruent, then the
quadrilateral is a parallelogram.
G
H
then Quad. EFGH is a parallelogram.
M
Theorem 4
E
F
If the diagonals of a quadrilateral bisect each
other, then the quadrilateral is a parallelogram .
then Quad. EFGH is a parallelogram.
EM GM and HM FM
4
5 ways to prove that a quadrilateral is a
parallelogram.
1. Show that both pairs of opposite sides are
. definition
2. Show that both pairs of opposite sides are ? .
3. Show that one pair of opposite sides are both
? and .
4. Show that both pairs of opposite angles are ? .
5. Show that the diagonals bisect each other .
5
Examples
Example 1
Find the value of x and y that ensures the
quadrilateral is a parallelogram.
y2
6x 4x8 2x 8 x 4 units
2y y2 y 2 unit
6x
4x8
2y
Find the value of x and y that ensure the
quadrilateral is a parallelogram.
Example 2
5y 120 180 5y 60 y 12 units
2x 8 120 2x 112 x 56 units
(2x 8)
120
5y