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### Unit 5: Lesson 3

Area of composite figures

# Finding area by rearranging parts

Sometimes it helps to rearrange the parts of geometric figures to find the area. That's what we're going to do here. Created by Sal Khan.

## Want to join the conversation?

• i dont understand any of this
• What don't you understand? If its why moving the shape works, then its because the area of the shape is only being shifted to another side of the object. This still counts as part of the area even though its shifted. The reason why you shift part of the are to another side is so that its easier to calculate.
• what im still confused i dont understand anything.
• well, they are showing how these different quadrilateral's area is being found. The green one can either be like blue(if you remove the extra triangles) or the red(if you finish the triangle by bringing up or down one.) and for the pink we have an extra that cant be finished, so it is left, and if you compare green and pink pink is bigger with the extra.

hope it is useful!
• With the pink one, why did he not count the 'extra'?
• Sal was desperately in search for the one similar to the green quadrilateral . So , after finding out that the green one had extra right angled triangle , he skipped that and went forward . Hope that helped.
• I have math homework that is about finding the area of a polygon, could you make a video on that please ?

thank you
• Finding the area of a polygon is quite simple. I'll explain how to do so here. Let's say we have a hexagon. Each side of the hexagon is 7 inches. The first step is to divide the hexagon into triangles and find one of their areas. Say the triangle had a base of 7in and a height of 4in. Figure out the area (which would be 14 sq in.) Now, multiply 14 by the amount of sides that the shape has. So 14x6, which is 84. Therefore, the area of the polygon is 84 square inches.

I hope this helped!
• i am so confused i know what to do but at the same time i do not how to have a shape that does not already have the base and height for me
'Liza and Abby plan to spread out blankets at a park for a picnic with some friends. The park is crowded, so they end up overlapping the blankets as is shown in the diagram.'

the top blanket is,

top: 5.7
left side: 5
bottom: 4

the side blanket is making the side of the other one make the corner a triangle and it forms a triangle that way.

and the bottom of the triangle is 5.7
the rectangle is
left side; 6
right side; 2
bottom; 4
• i dont understand any of this
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