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Angles and Triangles Terry Scates Newton, Kansas Instructor Notes • • • • • Subject Area(s): Math Grade level: 7th grade Lesson Length: 50 minute class period Synopsis: Name triangles by angles and sides. Objective/goals: Students will classify triangles according to types or angles and sides. (This PowerPoint presentation was designed as a supplemental piece to the presentation entitled Classifying Triangles by James Wiens for students in the special education math class.) Instructor Notes • Standard: ▲ identifies angle and side properties of triangles and quadrilaterals (KS standard 7.3.1.k3) • Pre-requisite skills: Vocabulary – Acute, Obtuse, Right, Equilateral, Isosceles, Scalene • TurningPoint functions: standard question slides • Materials: All instructional points and practice problems are provided within the power point slides. Practice questions are designed to be used with the TurningPoint clickers. (This PowerPoint presentation was designed as a supplemental piece to the presentation entitled Classifying Triangles by James Wiens for students in the special education math class.) Lesson Outline 1. 2. 3. 4. 5. Warm-up: Angle classification Setting the Stage: Guided practice: Turning Point Questions Independent practice: Paper & pencil Closure: Write about triangles What we already know about angles: An angle has two sides that share a common endpoint. What we need to know about angles: The point where the sides meet is called the vertex. What we need to know about angles: • Angles are measured in degrees, where 1 degree is one of 360 equal parts of a circle. Angles are classified according to their measure. An acute angle is less than 90° An obtuse angle is more than 90° A right angle is 90° Right Angle Find some examples of right angles in the classroom: Acute Angle Find some examples of acute angles in the classroom: Obtuse Angle Find some examples of obtuse angles in the classroom: Classify this angle: Classify this angle: a) Acute b) Right c) Obtuse 10 Countdown Classify this angle: a) Acute b) Right c) Obtuse 10 Countdown Classify this angle: a) Acute b) Right c) Obtuse 10 Countdown What we already know about triangles: • A triangle is a figure with three sides and three angles. • The symbol for triangle is What we need to know about triangles: • The sum of the measures of the angles of a triangle is 180°. • You can use this to find a missing angle measure in a triangle. Triangles can be classified by the measures of their angles. • An acute triangle has three acute angles. • An obtuse triangle has one obtuse angle. • A right triangle has one right angle. Triangles can also be classified by the lengths of their sides. • Sides that are the same length are congruent segments and are often marked by tick marks. • In a scalene triangle, all sides have different lengths. • An isosceles triangle has at least two congruent sides. • An equilateral triangle has all three sides congruent. Classify this triangle by angles and by sides 70 7 4 40 70 1. 2. 3. 4. 7 Acute / Isosceles Obtuse / Isosceles Acute / Scalene Obtuse / Scalene 10 Countdown Classify this triangle by angles and by sides 8 90 30 4 9 60 1. 2. 3. 4. Acute / Isosceles Right / Isosceles Acute / Scalene Right / Scalene 10 Countdown Classify this triangle by angles and by sides 6 14 130 15 35 18 1. 2. 3. 4. Acute / Isosceles Obtuse / Isosceles Acute / Scalene Obtuse / Scalene 10 Countdown Classify this triangle by angles and by sides 7 60 60 7 7 60 1. 2. 3. 4. Acute / Isosceles Right / Isosceles Acute / Equilateral Obtuse / Scalene 10 Countdown You are ready to try on your own! • Think about what you have learned. • Think about what you already knew. • Think about what you can teach others. Independent Practice Independent Practice Answer Key for Independent Practice A. Obtuse / Isosceles E. Obtuse / Isosceles B. Acute / Equilateral F. Acute / Equilateral C. Right / Isosceles G. Obtuse / Scalene D. Acute / Isosceles H. Right / Scalene Closure/Summary • Is the sum of the angles of an obtuse triangle greater than the sum of the angles of an acute triangle? Explain your answer. References Glencoe McGraw-Hill Math Connects Course 2, Study Guide and Intervention and Practice Workbook, 2008. Wiens, James, Classifying Triangles, PowerPoint presentation, November 2008.