6.5 Rhombi and Squares GEOMETRY
A rhombus is a parallelogram with four congruent sides
D IAGONALS OF A R HOMBUS Theorem 6.15: A parallelogram is a rhombus if and only if its diagonals are perpendicular.
Theorem 6.16: A parallelogram is a rhombus if and only if each diagonal bisects a pair of opposite angles.
Theorem 6.19 If one pair of consecutive sides of a parallelogram are congruent, then the parallelogram is a rhombus.
E XAMPLE 1 Find x, y, and z. (6x + 30)° ABCD is a rhombus. C B A D 18 2z-2 (7y -2)° (3y +10)°
A square is a parallelogram with 4 congruent sides and 4 right angles.
Theorem 6.20 If a parallelogram is a rhombus and a rectangle, then it is a square.
E XAMPLE 2 ABCD is a square.
Venn Diagram parallelograms rhombirectangles squares
E XAMPLE 3 Determine if parallelogram QRST is a rhombus, rectangle, or square. Q(-2,-1), R(-1,2), S(4,1), T(3,-2)
H OMEWORK Worksheet and… Page 431: (7-12, 23-33, 55-60) all