# Using a Formula to Find the Surface Area of Prisms

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## Objective

SWBAT find the surface area of prisms using a formula

#### Big Idea

Students will use their knowledge of nets to help them find an algebraic way of finding the surface area

## Lesson Beginning

5 minutes

In this section, I present the students with a real-world tie in.  I’ll show a box that is in shrink wrap.  I’ll then ask: “Why would I need to know the surface area of this prism?” Students hopefully will relate the surface area to the amount of wrapping.  Tie this concept into how this would need to be calculated for an item that is mass produced.  I will then ask the essential question:  How can you find the surface area of prisms using a formula?  I remind students that we have already found the surface area of prisms by finding the sum of the areas of all faces.  Today we use a formula.  All surfaces area formulas of prisms summarize to:  Surface area = area of bases + areas of lateral faces.  Throughout the lesson students have a chance to practice MP2 as they represent solutions using mathematical symbols (formulas).  For example, when students are confronted with an expression like 2lw, they see that this represents the total area of two opposite faces of a rectangular prism.  In addition, students are solving problems using algebra as a model (MP4).

## Lesson Middle

35 minutes

This part of the lesson is the “I”, “WE”, and “YOU” of the lesson.  In the “I” section I present two examples.  Students are to watch my example and then fill in notes when instructed.  In the “WE” section, students work together to solve problems that are similar to the examples.  They are to show work  in a manner similar to the model given in the “I” section.  In the “YOU” section, it is all independent work.  I will have identified students who need support at this point.  Struggling students will be reminded to follow the steps in the examples first before asking for help.  When nearly all have finished the main independent practice, we’ll go over solutions as needed.

10 minutes