Cuboid Surface Area: Analyzing a Three-Dimensional Rectangular Prism

Surface Area Formula with Three-Dimensional Geometry

Look at the cuboid below:

cccaaabbb

Choose the correct representation of its surface area.

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Express the surface area of the box
00:03 Now we'll use the formula to calculate the surface area of a box
00:20 We'll substitute appropriate values and solve to find the surface area
00:58 And this is the solution to the problem

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Look at the cuboid below:

cccaaabbb

Choose the correct representation of its surface area.

2

Step-by-step solution

To find the surface area of a cuboid, we consider its six rectangular faces. A cuboid has three pairs of opposite faces. Each pair of faces shares the same area.

The surface area S S of a cuboid with dimensions a a , b b , and c c is calculated by finding the area of each of these rectangular faces and then summing them up. Specifically, we consider:

  • The area of the first pair of opposite faces with dimensions a a and b b is ab ab .
  • The area of the second pair of faces with dimensions b b and c c is bc bc .
  • The area of the third pair of faces with dimensions a a and c c is ac ac .

The total surface area is thus given by the formula:

S=2(ab+bc+ac) S = 2(ab + bc + ac)

By analyzing the provided choices, it's clear that the correct formula for the surface area of the cuboid is 2(a×b+b×c+a×c) 2(a\times b + b\times c + a\times c) .

Therefore, the solution to the problem is 2(a×b+b×c+a×c) 2(a \times b + b \times c + a \times c) .

3

Final Answer

2(a×b+b×c+a×c) 2(a\times b+b\times c+a\times c)

Key Points to Remember

Essential concepts to master this topic
  • Formula: Surface area equals twice the sum of three face areas
  • Technique: Calculate ab + bc + ac, then multiply by 2
  • Check: Count six faces: two of each type equals 2(ab + bc + ac) ✓

Common Mistakes

Avoid these frequent errors
  • Confusing surface area with volume formula
    Don't use a × b × c = wrong formula for surface area! This gives you volume (space inside), not surface area (outside covering). Always use 2(ab + bc + ac) for the total area of all six faces.

Practice Quiz

Test your knowledge with interactive questions

A cuboid is shown below:

222333555

What is the surface area of the cuboid?

FAQ

Everything you need to know about this question

Why do we multiply by 2 in the surface area formula?

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Because a cuboid has six faces that come in three pairs! Each pair has identical areas: two faces with area ab, two with area bc, and two with area ac. So we calculate one of each type, then multiply by 2.

How is this different from finding volume?

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Surface area measures the total area of the outside surfaces (like wrapping paper needed). Volume measures space inside using a×b×c a \times b \times c . They're completely different measurements!

What if the cuboid has different dimensions like length, width, height?

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It doesn't matter what you call them! Whether it's a, b, c or length, width, height, the formula stays the same: 2(lw+wh+lh) 2(lw + wh + lh) .

Can I add the areas in a different order?

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Yes! Addition is commutative, so ab + bc + ac equals bc + ac + ab. The order doesn't matter as long as you include all three different face areas.

Why isn't the third answer choice correct?

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Choice 3 uses 2[(a+b)×(b+c)×(a+c)] 2[(a+b) \times (b+c) \times (a+c)] , which adds dimensions before multiplying. This doesn't represent any real geometric measurement and gives a much larger, incorrect result.

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