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## Basic geometry and measurement

### Course: Basic geometry and measurement>Unit 9

Lesson 2: Surface area with nets

# Surface area of a box using nets

Discover the surface area of a cereal box by visualizing a net. Cut and flatten the box to create a 2D shape. Measure the dimensions, calculate the area of each section, and add them up for the total surface area. Fun and practical!

## Want to join the conversation?

• You don't have to use a net. S=2lw+2wh+2lh
• Or 2(lw+wh+lh)
• At is he drawing in the height?
• Sort of, he is drawing what cannot be seen, the height of the back of the cereal box. Dotted lines mean behind the shape.
• this is hard can some one help
• If you find this method hard, try the previous video.
Or use the formula 2(lb+bh+lh)
where l is length , b is breadth and h is height.
• Ok, here's a question. Why do we need the use of nets in real life? Is it just the standard they added to extend school? BTW: Sal makes me want to learn more about cereal boxes and math :-)
• do these types of methods also work in real life?
• If you want to find a way to break down boxes in a cool way then yes.

If you mean volume then that is very important in life. If you get a package that has a volume of 20 ft^3 or something, then what's in there has to be kinda big, heavy, or fragile because you would also need the wrapping to protect it if it's glass or whatever

So to answer your question, yes. If you mean geometry in general then that's also "Yes".
• Sal is the best. Khan academy videos are ta best
• You should write this post in the Tips and Thanks section.
• How do you do this again
• Imagine that you are unfolding a polyhedron to be flat.

It might help to draw what that looks like, you might need to practice a few times, but you should get a hang of it.

After you have the net of your polyhedron, then find the area by breaking it down into shapes that you know how to take the area of, such as rectangles and triangles.

Then, add the total area together to get your answer, which is equal to the surface area of the polyhedron.
• I don't know how to break it up