Lesson 18

Finding the surface area of triangular prisms using a net

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SWBAT find the surface area of triangular prisms using a net

Big Idea

Students use nets to visualize dimensions of bases and lateral faces of a triangular prism.

Lesson Beginning

20 minutes

*Creating Nets

 I start the lesson by giving every student a pair of scissors and a net on cardstock similar to the one shown in the resource.  I have noticed that students often have difficulty seeing the faces of a triangular prism when it is represented on a piece of paper.  Constructing the model (MP5) helps students make the connections.  I’ll give the students about 3 minutes (timed) to cut out their net and fold on the dotted lines.  I will have a completed net to show students how their net should look.  Students will not tape the nets together as we will need to open and close them throughout parts of the discussion.


Now that we have our nets, we use them to answer the discussion questions.  I’ll pose each question as a think-pair-share.  I will walk around during the pair to hear what students are saying and to pose the question to pairs that seem reticent to speak.  I will try to keep a brisk pace as we work through each question.  The questions are designed to get students to see how the parts of the prism are related. 

*Guided Problem Solving

I will now guide the students into finding the surface area of the net represented in their hands on their paper.  First we will find the area of the bases.  I will look to make sure students identify correctly the base and the height of the base.  Students will be confused by the fact that a triangular prism has 2 bases and 2 heights – one set belonging to the prism itself and the other belonging to the base shape.  We will then find the area of the lateral faces.  I hope by now students will begin to see that each lateral face has dimensions from one side of the triangle and the prisms height.  

Exit Ticket

15 minutes

After making sure students have solved the problems correctly we will summarize.  I will cold card students with the discussion questions.  If a student has a misconception they are not off the hook.  I will call on another student to help the student, but ultimately that student will need to answer the question(MP3).  Students will then have the rest of the time to solve 2 triangular prism problems.  I have included a composite shape at the end as a pre-assessment of future lessons.