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Lesson 5: Nets of 3D figures

# 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)
• 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.
• 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.
• 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 :-)
• Most boxes are flat when they are produced, think of pizza boxes, the ppl at the pizza shops fold the boxes. They need to know the dimensions to order the proper sizes.

When building Wood Framed Structures usually the walls are made on the ground first then lifted up into position. so the "net" is made first before the building takes shape
• Why can’t you just multiply height times width times base?
• If you multiply these three, you are finding the volume, not surface area.
• 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.