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Surface Area of 3D Figures

Teaching about two topics

Sean Moss

on 18 March 2011

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Transcript of Surface Area of 3D Figures

Welcome to Introduction to 3D Shapes. Today we'll be learning about the surface area of 3D figures. TAking the Surface area of a 3D shape is the same as finding the surface area of a 2D shape. Just with more sides. If one side is 6 cm by 6 cm then the shape is 36 cm^2 6 6
If you have a Rectangular Prisim. You have 6 surface area's to look at. For a rectangular prism at least two sides are exactly the same So if 2 sides were 3x2 cm then its
3x2=6 then 6x2=12cm^2 THen the other two sides are 2x4 so its 2x4=8 and two sides makes it 2x8=16cm^2. Then the last two are 3x4. 3x4=12 12x2 = 24cm^2 Now just add them all up. 12+16+24=52cm^2 Now for something a little more challenging. The area of a circle is just Pi r^2 correct? So if the radius is 5 cm then the Area is 25pi cm^2 You can leave that way or multiply by pi which would be about 78.5398163cm^2 Now for a cylinder there is three pieces. The top bottom and middle. If you break it down then there's two circle's and a rectangle thats coiled up. The height of the circle is one dimention and the circumfrence is the other. The circumfrence of a circle is the diamater times Pi. So the length of the rectangle is 10pi. So 10pi times 8 is 80pi. That plus the surface area's of the two circles would be 80pi+25pi+25pi=130pi cm^2 or about 408.407045cm^2. NowNo Now let's try one more Now we have a right square pyramid. The base is a square and it comes to a point with 4 congruent triangles. The base of the pyramid is the square which is easy. 4x4=16cm^2 The sides of the pyramid are triangles. The Surface Area of a triangle is 1/2 base times height. So 4x10=40 half of 40 is 20. Then since there are four sides its 20x4=80cm^2 Now you add. 16+80=96cm^2 Thanks for watching. This has been... Brought to you
Sean Moss.
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