6 5 Rhombi and Squares ThenNow You determined

6. 5 Rhombi and Squares

Then/Now You determined whether quadrilaterals were parallelograms and/or rectangles. • Recognize and apply the properties of rhombi and squares. • Determine whether quadrilaterals are rectangles, rhombi, or squares.

Vocabulary • Rhombus: a parallelogram with all four sides congruent

Vocabulary • Square: a parallelogram with four congruent sides and four right angles

Theorem 6. 15: Vocabulary Diagonals of a Rhombus #1 If a parallelogram is a rhombus, then its diagonals are perpendicular.

Theorem 6. 16: Vocabulary Diagonals of a Rhombus #2 If a parallelogram is a rhombus, then each diagonal bisects a pair of opposite angles.

Theorem 6. 17: Vocabulary Condition #1 for a Rhombus If the diagonals of a parallelogram are perpendicular, then the parallelogram is a rhombus. *Converse of 6. 15

Theorem 6. 18: Vocabulary Condition #2 for a Rhombus If one diagonal of a parallelogram bisects a pair of opposite angles, then the parallelogram is a rhombus. *Converse of 6. 16

Theorem 6. 19: Vocabulary Condition #3 for a Rhombus If one pair of consecutive sides of a parallelogram are congruent, then the parallelogram is a rhombus.

Theorem 6. 20: Vocabulary Square Conditions If a quadrilateral is both a rectangle and a rhombus, then it is a square.

Example 1 A Use Properties of a Rhombus A. The diagonals of rhombus WXYZ intersect at V. If m WZX = 39. 5, find m ZYX. Answer: m ZYX = 101

Example 1 B Use Properties of a Rhombus B. ALGEBRA The diagonals of rhombus WXYZ intersect at V. If WX = 8 x – 5 and WZ = 6 x + 3, find x. Answer: x=4

Example 1 A A. ABCD is a rhombus. Find m CDB if m ABC = 126. A. m CDB = 126 B. m CDB = 63 C. m CDB = 54 D. m CDB = 27

Example 1 B B. ABCD is a rhombus. If BC = 4 x – 5 and CD = 2 x + 7, find x. A. x = 1 B. x = 3 C. x = 4 D. x = 6

Rectangle Rhombi

Example 2 Proofs Using Properties of Rhombi and Squares Is there enough information given to prove that ABCD is a rhombus? Given: ABCD is a parallelogram. AD DC Prove: ABCD is a rhombus A. Yes, if one pair of consecutive sides of a parallelogram are congruent, the parallelogram is a rhombus. B. No, you need more information

Example 3 Sachin has a shape he knows to be a parallelogram and all four sides are congruent. Which information does he need to know to determine whether it is also a square? A. The diagonal bisects a pair of opposite angles. B. The diagonals bisect each other. C. The diagonals are perpendicular. D. The diagonals are congruent.