Find the Area of Figures with Missing Sides

Grade 3: Unit 2: Lesson 14

Let’s find the �area of figures with missing side lengths!

Notice and Wonder: Mystery Sides

Warm-Up

What do you notice? What do you wonder?

Let’s Talk About It!

• Do you think we could still find the area of this figure even though some of the side lengths are missing? Why or why not?�
• How would you find the missing side lengths?

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The Mystery Side

Activity 1

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Tyler says that the missing side length is 5 meters because it looks longer than the sides that are 4 meters long.��Do you agree or disagree? Be prepared to explain your reasoning.

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Let’s Talk About It!

• What strategies did you or your partner use to find the missing side length?�

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Practice with Mystery Sides

Activity 2

• MLR 8: Discussion Supports
• Engagement

Find the area of each figure. Explain or show your reasoning.

Find the area of each figure. Explain or show your reasoning.

Let’s Talk About It!

◦ What missing side had to be found to use this strategy? How did you find the missing side length?

◦ After you knew the missing side lengths, how did you find the area?

◦ What is the expression we would write to match how you decomposed the figure?

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Lesson Synthesis

• Today we learned that we can find missing side lengths in figures. What is it about the structure of the figures we saw in this lesson that helps you find missing side lengths?

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• How do you like to find the area of these figures after you know the side lengths?

Mystery Side Area

Cool-Down

Find the area of the figure. Explain or show your reasoning.

Cool-Down: Mystery Side Area

Image Citations

https://pixabay.com/vectors/magnifying-glass-magnify-glass-1293096/

https://giphy.com/gifs/cbs-united-states-of-al-usofal-cbs-2e3HWNOYslENp5rF73

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