Composite objects

When calculating the volume or surface area of a composite solid, split the object up into sections and calculate each element separately.

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Surface area of a composite object
To calculate the surface area of this object, start by identifying the dimensions of each surface.
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Surface area of a composite object
The front face and the back face are identical. Once we have calculated the area of one, we can double it.
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Surface area of a composite object
Split the L-shape into two rectangles and add together the areas: Area = 5 × 11 + 15 × 4 = 55 + 60 = 115 cm squared, Area of front and back = 2 × 115 = 230 cm squared.
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Surface area of a composite object
The area of the bottom face is equal to the two sections on the top of the object.
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Surface area of a composite object
Area = 6 × 20 = 120 cm squared, Area of the top and bottom = 2 × 120 = 240 cm squared.
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Surface area of a composite object
The area on the left hand side of the object is equal to the two shaded regions on the right hand side.
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Surface area of a composite object
Area = 11 × 6 = 66 cm squared, Area of left and right = 2 × 66 = 132 cm squared.
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Surface area of a composite object
The total surface area = 230 + 240 + 132 = 602 cm squared.