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Learn the properties of parallelograms, including their sides, angles, and diagonals. Discover the theorems that govern these properties and apply them in solving problems. Homework exercises included.
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Geometry Lesson 6 – 2 Parallelograms Objective: Recognize and apply properties of the sides of angles of parallelograms. Recognize and apply properties of the diagonals of parallelograms.
Parallelograms • What is a parallelogram? • A quadrilateral with both pairs of opposite sides parallel. • To name a parallelogram:
Theorems:Properties of Parallelograms • Theorem 6.3 • If a quadrilateral is a parallelogram, then its opposite sides are congruent.
Theorem • Theorem 6.4 • If a quadrilateral is a parallelogram, then its opposite angles are congruent.
Theorem • Theorem 6.5 • If a quadrilateral is a parallelogram, then its consecutive angles are supplementary.
Theorem • Theorem 6.6 • If a parallelogram has one right angle, then it has four right angles.
In parallelogram ABCD, suppose the measure of angle A is 55, segment AB is 2.5 feet, and segment BC is 1 foot. Find each measure. • Find DC 2.5 180 – 55 = 125 55
Theorems:Diagonals of Parallelograms • Theorem 6.7 • If a quadrilateral is a parallelogram, then its diagonals bisect each other.
Theorem • Theorem 6.8 • If a quadrilateral is a parallelogram, then each diagonal separates the parallelogram into two congruent triangles.
5x = 27 If QRST is a parallelogram, find the following. • Find x • Find y • Find z Opps. Sides equal x = 5.4 Diagonals bisect 2y – 5 = y + 4 y = 9 Alt. Interior angles are congruent. 3z = 33 z = 11
Find the value of each variable in the parallelograms. 3z – 4 = z + 5 4x + 2x – 6 = 180 6x – 6 = 180 2z = 9 6x = 186 z = 4.5 x = 31 y + 8 = 5y 2 = y
Determine the coordinates of the intersection of the diagonals of parallelogram FGHJ with vertices F (-2, 4) G (3, 5) H (2, -3) and J (-3, -4) • What do you know about the diagonals of a parallelogram? • Since we know they bisect what is a good point to find? • Find the Midpoint of the diagonals: Double check:
Determine the coordinates of the intersection of the diagonals of RSTU with vertices R (-8, -2) S (-6, 7) T (6, 7) and U (4, -2)
1. 1. Given 2. Opp. Sides congruent. 2. 3. 3. Transitive
Homework • Pg. 403 1 – 6 all, 10 – 22 E, 44 – 60 E