# Lesson: Sum of Angles in Polygons

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### Lesson Objective

SWBAT discover the sum of angles in any polygon using the triangle method. SWBAT use the sum of angles in a polygon to determine the missing angle.

### Lesson Plan

Element/Time

Lesson Steps

Do Now

(8:30 – 8:40)/(10:00 –10:10)

·         T displays 4 review problems

·         S complete problems independently on do now sheet

·         T walks around to check hw/help students with do now questions

·         T/S review problems together

·         S correct their work to reflect the correct answers

HW Check

·         T displays correct answers and work

·         S correct work with colored pencil  T walks around to review specific students work

·         T/S review 3 questions

Mini Lesson

(8:50 – 9:25)/(10:20 – 10:55)

·         Review key idea from previous day – triangles equal 180°

·         Tell students that using just that information we can find the sum of angles in any polygon

·         T demonstrates using the triangle method to find the sum of angles in any polygon but splitting the polygon into triangles and then multiplying the number of triangles by 180.

·         T and S will practice first dividing polygons into triangles

·         S will practice working to find the sum of angles within different polygons.

·         T and S will conclude at the end of class that any quad will have 360, pentagon will have

Skills Time

(9:35- 9:50) /(11:05-11:25)

·         See if we can figure out a rule (using algebra) to find out the sum of angles in any polygon.

Sum = 180 (n – 2)

 Name Number of Sides Sum of Angles Triangle 3 180 Quad 4 360 Pent 5 540

·         Review week of angles

·         Read Sir Cumference and  the Great Knight of Angleland

·         Make sure flip books are up to date

### Lesson Resources

 sum of angles notes 837 quiz sum of angles 721 sum of angles polygons organizer 902 Lesson on Sir Cumference and the Great Knight 2007 Quads and Angle Sums 2007 Quads and Angle Sums Homework 2007 U9.L4.SHAPES.Interior.Angle.Sums.docx 628 U9.L4.SHAPES.Interior.Angle.Sums.kh.docx 452