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1. 1. Lesson 8.3 , For use with pages 416-419 Classify the triangle by its side lengths. 1. 2.
2. 2. Lesson 8.3 , For use with pages 416-419 Classify the triangle by its side lengths. ANSWER isosceles 1. ANSWER equilateral 2.
3. 3. Quadrilaterals Section 8-3 P. 416-419
4. 4. Essential Questions <ul><li>Why is it important to be able to identify congruent triangles in everyday life? </li></ul><ul><li>Where in real life can you use the properties of isosceles and equilateral triangles? </li></ul><ul><li>How are the relationships between lines and planes used in the real world? </li></ul><ul><li>What areas in the real world are properties of parallel lines important? </li></ul>
5. 5. Quadrilaterals <ul><li>Quadrilaterals are named for the number of sides. Quad means four, so a quadrilateral is 4-sided figures. </li></ul><ul><li>Some quadrilaterals are very perfect – like a square, and others are very generic. </li></ul>
6. 6. <ul><li>Quadrilateral = a closed figure made with four sides that are line segments. </li></ul><ul><ul><li>The sum of the four angles in any quadrilateral equals 360 degrees. </li></ul></ul><ul><li>Trapezoid = a quad. with exactly ONE PAIR of parallel sides. </li></ul><ul><li>Parallelogram = two pairs of parallel sides </li></ul><ul><li>Rhombus = parallelogram with 4  sides </li></ul><ul><li>Rectangle = quad. with 4 right angles </li></ul><ul><li>Square = a rectangle with 4  sides </li></ul>
7. 7. Quadrilaterals Parallelograms Rectangle Square Rhombus Trapezoid
8. 8. Diagonal <ul><li>A diagonal of a polygon connects two vertices that do not share a side. </li></ul><ul><li>Trapezoid ABCD, name the diagonals </li></ul>A B C D Diagonal AC
9. 9. The quadrilateral is a parallelogram with 4 sides of equal length. So, it is a rhombus. EXAMPLE 1 Classifying a Quadrilateral Classify the quadrilateral. The quadrilateral is a parallelogram with 4 sides of equal length and 4 right angles. So, it is a square. a. b.
10. 10. Quadrilaterals <ul><li>As with triangles, all quadrilaterals have a common characteristic. The sum of the 4 angles in a quadrilateral always equals exactly 360 degrees. </li></ul>90 x 4 = 360 2 @ 45 = 90 2 @ 135 = 270 Total sum of 360
11. 11. EXAMPLE 2 Finding an Unknown Angle Measure SOLUTION The sum of the angle measures is 360 . Add. Subtract 309 from each side. Find the value of x . x + 51 + 129 + 129 = 360 x + 309 = 360 = x 51
12. 12. GUIDED PRACTICE for Examples 1 and 2 ANSWER x = 65 Use the figure at the right. 1. Classify the quadrilateral. ANSWER The quadrilateral is a trapezoid with exactly 1 pair of parallel sides. 2. Find the value of x .
13. 13. Classzone.com <ul><li>Go to the 8 th grade math book </li></ul><ul><li>Animations </li></ul><ul><li>Click on the left side on Chapters 7-9 </li></ul><ul><ul><li>Chapter 8: Drawing Quadrilaterals </li></ul></ul><ul><ul><ul><li>Chapter 8: Playing Golf with Angles </li></ul></ul></ul>
14. 14. Homework <ul><li>Assignment: p. 417 – 418 #1-14, 19-24 </li></ul><ul><li>When classifying, be as specific as possible and you only need to use one name. </li></ul><ul><li>#6-8 You do NOT need to measure the quadrilaterals. </li></ul>