Lesson 2

Perimeter of Irregular Rectilinear Shapes

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SWBAT find the perimeter of rectilinear shapes by determining and summing the lengths of all sides

Big Idea

Students use the properties of rectangles to discover missing dimensions.


10 minutes

I will cold call students on questions about the previous day.  What measurements did we find?  Define those measurements.  What part of the bumper car track represented the perimeter?  What part represented the area? I will then say today we will only be focused on perimeter.  I will show students the exit ticket so they can see the criteria for success.


I will then introduce the example problem.  Before going over the steps, I will ask students to discuss the essential question.  With the example I will ask students to identify what information is missing and how can we determine the missing information.  Specifically, as all shapes are rectilinear, how can we use the properties of rectangles to help find the lengths of missing sides?  This gives students a chance to make sense of the problem (MP1) before I provide steps. Use language about rectangles to justify their answers gives students a chance to practice precision in their language (MP6).  I will then see if students can fill in the missing blanks of the steps before providing them.  I will then use the steps to model how to find the perimeter.

Guided Practice

5 minutes

Students will use the example problem, steps, and their neighbors as a resource.  I will insist on students using these resources before asking me for help.  


Independent Practice

15 minutes

 Once it is clear the majority have successfully solved the problem, students will begin working independently.

I will only provide intervention to those students that struggled with the guided practice.  Otherwise, I will remind students to use their notes.   

Lesson Summary + Exit Ticket + Homework

10 minutes

We will briefly go over solutions as needed.  If there are major difficulties I will have the class transfer the image to graph paper.  Students will then take the exit ticket.