Learn about polygons, parallelograms, and rhombuses, including their definitions, properties, and theorems. Explore how to identify and prove these shapes using coordinates and angle measures.
01 / 65Properties of Polygons: Polygons, Parallelograms, and Rhombuses
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Properties of Polygons: Polygons, Parallelograms, and Rhombuses
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Poly Many A polygon is a plane figure that meets the following conditions: 1) It is formed by three or more segments called sides such that no two sides with a common endpoint are collinear. 2) Each side intersects exactly two other sides, one at each endpoint.
Names of polygons # of sides Name 3 Triangle 4 Quadrilateral 5 Pentagon 6 Hexagon 8 Octagon 10 decagon 12 dodecagon n n-gon When naming polygons, you list the vertices in order! R P T E L B Hexagon PRTBLE Or Hexagon TBLEPR Or other names
Interior angles of a Quadrilateral The sum of the measures of the interior angles of a quadrilateral is 360o. Solve for x xo xo x+20o x+20o 2xo 2xo 100o 100o
Opposite sides are parallel, then it’s a ||-gram by def. S 3 T 2 1 R 4 Q THRM 6.6 If both pairs of opposite sides of a quad are congruent, then the quadrilateral is a parallelogram. THRM 6.8, If an angle of a quad is supplementary to both its consecutive angles, then the quadrilateral is a ||- gram THRM 6.7 If both pairs of opposite angles of a quadrilateral are congruent, then the quadrilateral is a ||-gram THRM 6.9 If the diagonals of a quad bisect each other, then the quadrilateral is a ||-gram
Let’s discuss how to prove two of these theorems S 3 T 2 1 R 4 Q THRM 6.6 If both pairs of opposite sides of a quad are congruent, then the quadrilateral is a parallelogram. M THRM 6.9 If the diagonals of a quad bisect each other, then the quadrilateral is a ||-gram
Prove that the following coordinates make a parallelogram by the given theorems\definitions using slope formula and distance formula. A B (-1, 3) (3, 2) D C (-4, -1) (0, -2) Opposite sides are parallel, then it’s a ||-gram by def. One pair of opposite sides are both CONGRUENT and PARALLEL. The diagonals of a quad bisect each other
Rectangle – Quad with 4 rt angles. Rhombus – Quad with 4 congruent sides Square – 4 rt angles AND 4 congruent sides, It’s a rectangle AND a rhombus!! Why are these parallelograms?
World O’ Parallelograms Answer with always, sometimes, or never A Rhombus is a Square Always Sometimes Never A Square is a Parallelogram Always Sometimes Never
Corollaries Rhombus Corollary A quadrilateral is a rhombus iff it has four congruent sides. Rectangle Corollary A quadrilateral is a rectangle iff it has four right angles. Square Corollary A quadrilateral is a square iff it is a rhombus and a rectangle.
A D M B C A B D C Thrm 6.11 A ||-gram is a rhombus iff its diagonals are perpendicular. Thrm 6.12 A ||-gram is a rhombus iff each diagonal bisects a pair of opposite angles.
A quadrilateral with EXACTLY one pair of parallel sides is called a TRAPEZOID. The parallel sides are called BASES. The other sides are LEGS Trapezoids have two pairs of base angles. ISOSCELES TRAPEZOID – LEGS are CONGRUENT! KITE – A quadrilateral with two pairs of consecutive sides, BUT opposite sides aren’t congruent.
Theorem 6.14 Base angles of an isosceles trapezoid are congruent. B A X Y Z ONLY TRUE FOR ISOS TRAPEZOID, NOT REGULAR TRAPEZOID! Congruent, opp sides ||-gram congruent. Transitive to work all sides congruent. Corresponding, base angles thrm, transitive. Same side interior angles, measure, supp, subtraction.
C Theorem 6.18 If a quadrilateral is a kite, then its diagonals are perpendicular B D A Theorem 6.18 If a quadrilateral is a kite, then EXACTLY one pair of opposite angles are congruent. C B D A