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### Course: Basic geometry and measurement>Unit 8

Lesson 4: Area of composite figures

# Area of composite shapes

We can sometimes calculate the area of a complex shape by dividing it into smaller, more manageable parts. In this example, we can determine the area of two triangles, a rectangle, and a trapezoid, and then add up the areas of the four shapes to get the total area. Created by Sal Khan.

## Want to join the conversation?

• Can't you just think of the bottom part as a trapezoid? You can add 6.5 and 3.5 and divide by 2 and multiply that by 9 to get the bottom part. That would save you the hassle of finding the triangle's and the rectangle's area.
• There can be many ways to do composite figures, and your way is just as valid since you divide it into known shapes especially since the area of trapezoids is the first in this string of videos. For fun, I might start with a large 10 by 9 rectangle and take away the three triangles that are cut off from the corner 90 - 3.5 - 13.5 - 12.25 = 60.75.
• What if the shape has a half circle in it?
• Then use the circle formula and divide it by 2.
• "Say when I grow up, what is this useful for?"
• geometry is useful for architecture, design,renovation, building, art, and sometimes just daily activities. This information will also be helpful if you end up needing or wanting to help someone else that has curriculum revolving around this subject. There many uses for geometry in life.
• I don't understand how to do this can someone explain?!
-\'_'/-
• So what he's saying is that you need to break up the shape to make it easy to divide
• can some one explain i'm not giving up but i want to can any one help. Thanks.
• So to find the area of an oddly shaped figure that you don't have a formula for, you split it into lots of smaller figures that you already know how to find the area of. Then you add them all together to find the total area of the original larger figure. Does that make sense? Let me know if there's anything you still don't understand.
• im brainig so hard my think hurts.
• I am sooooo confused about why he did 1 half times 7
• He is doing the formula for a triangle, 1/2(base)(height). This can be done in different orders. You can find (base)(height) and then divide by 2, or you can find 1/2(base) and multiply by (height) (or vice versa), which is what he is doing. I've always done it the first way, and this may be the way you do it, which is why you don't recognize his method.
(1 vote)
• am i slow, or did this video make no sense at all