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# What would Justin do? Algebra outside of “the box”

Download Presentation ## What would Justin do? Algebra outside of “the box”

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1. What would Justin do? Algebra outside of“the box” WATERTOWN MIDDLE SCHOOL Lesson Study Open House April 11, 2006

2. Let’s go back to Justin…

3. Calculating surface area (of a cube)

4. Justin’s way (cube)

5. Calculating surface area of a rectangular prism • S = 2lw + 2lh + 2wh

6. Justin’s way: • S = 2lw + 2lh + 2wh • S = l(2w + 2h) + 2wh

7. How did you get your answer?

8. Try to find two other correct algebraic expressions for the number of exposed faces in a prism formed by N cubes - by thinking about the problem differently.(i.e.: what would Justin do?)

9. How might you get…? • 6N –2(N –2) – 2

10. How might you get…? • 6N –2(N –2) – 2 • N+N+N+N+2

11. How might you get…? • 6N –2(N –2) – 2 • N+N+N+N+2 • 5N –2(N –2)

12. What happens if, instead of a prism that is one cube wide, we create prisms that are two cubes or three cubes wide?

13. :

14. :

15. How can you describe the exposed faces of a prism in terms of the width (W) AND the length (N)?

16. How can you describe the exposed faces of a prism in terms of the width (W) AND the length (N)? • 2WN + 2W + 2N

17. How can you describe the exposed faces of a prism in terms of the width (W) AND the length (N)? • F(W,N) = 2WN + 2W + 2N (A function of two variables?!)

18. Determine the number of exposed faces of a prism that is N cubes long, W cubes wide, and H cubes high.