Tests for Parallelograms

Proving Quadrilaterals as Parallelograms5 ways

If both pairs of opposite sides of a quadrilateral are parallel, then the quadrilateral is a parallelogram .

From definition:

H G

E F

Proving Quadrilaterals as Parallelograms

If both pairs of opposite sides of a quadrilateral are congruent, then the quadrilateral is a parallelogram .

Theorem 1:

H G

E FIf one pair of opposite sides of a quadrilateral are both congruent and parallel, then the quadrilateral is a parallelogram .

Theorem 2:

If EF GH; FG EH, then Quad. EFGH is a parallelogram.

If EF GH and EF || HG, then Quad. EFGH is a parallelogram.

Theorem:

If both pairs of opposite angles of a quadrilateral are congruent, then the quadrilateral is a parallelogram.

Theorem 3:

If the diagonals of a quadrilateral bisect each other, then the quadrilateral is a parallelogram .

Theorem 4:

H G

EF

M

,If H F and E G

then Quad. EFGH is a parallelogram.

intIf M is themidpo of EG and FH

then Quad. EFGH is a parallelogram. EM = GM and HM = FM

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 .

Examples ……Find the value of x and y that ensures the quadrilateral is a parallelogram.

Example 1:

6x4x+8

y+2

2y

6x = 4x+8

2x = 8

x = 4 units

2y = y+2

y = 2 unit

Example 2: Find the value of x and y that ensure the quadrilateral is a parallelogram.

120° 5y°

(2x + 8)°2x + 8 = 120

2x = 112

x = 56 units

5y + 120 = 180

5y = 60

y = 12 units