Comparing Surface Areas of Two Orthohedra: 1×2×3 Unit Analysis

Surface Area Formulas with Identical Dimensions

Look at the two orthohedra below:

111222333222111333

Are the surface areas of the two orthohedra the same or different?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Are the surface areas of the boxes equal?
00:03 Now let's use the formula to calculate the surface area of a box
00:22 For each box, let's write down the dimensions
00:51 Now let's substitute appropriate values in the formula for both boxes
01:19 Let's compare the calculations, and we'll see they're equal
01:28 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Look at the two orthohedra below:

111222333222111333

Are the surface areas of the two orthohedra the same or different?

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Step 1: Determine the dimensions of each orthohedron from the diagram.
  • Step 2: Calculate the surface area for each cuboid using the formula.
  • Step 3: Compare the calculated surface areas.

Now, let's work through each step:

Step 1: Identify the Given Dimensions
From the visual data, we note that the dimensions of the first orthohedron are given as 1, 2, and 3, while the second orthohedron has the same visual size with similar digits 1, 2, and 3 marked, suggesting identical measurements for each dimension.

Step 2: Calculate the Surface Area for Each Cuboid
Utilize the surface area formula for cuboids:

SA=2(lw+lh+wh) SA = 2(lw + lh + wh)

For Both Orthohedra, Given Dimensions:

  • Length (l l ): 1 unit
  • Width (w w ): 2 units
  • Height (h h ): 3 units

The surface area calculation will be:

SA=2(12+13+23) SA = 2(1 \cdot 2 + 1 \cdot 3 + 2 \cdot 3) =2(2+3+6) = 2(2 + 3 + 6) =211 = 2 \cdot 11 =22 square units = 22 \text{ square units}

As both cuboids have the same dimensions, their surface area calculations yield identical results.

Step 3: Compare Surface Areas
Since both orthohedra compute to the same total surface area of 22 square units, we conclude their surface areas are the same.

Therefore, the solution to the problem is The same.

3

Final Answer

The same.

Key Points to Remember

Essential concepts to master this topic
  • Formula: Surface area = 2(lw + lh + wh) for rectangular prisms
  • Technique: Calculate SA = 2(1×2 + 1×3 + 2×3) = 2(11) = 22
  • Check: Same dimensions mean same surface area regardless of orientation ✓

Common Mistakes

Avoid these frequent errors
  • Assuming different orientations have different surface areas
    Don't think rotating a 1×2×3 box changes its surface area = wrong conclusion! The formula uses all three dimensions equally, so orientation doesn't matter. Always remember that surface area depends only on the actual measurements, not how the shape is positioned.

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 both orthohedra have the same surface area if they look different?

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Great observation! Both shapes have identical dimensions: 1×2×3 units. Even though they're oriented differently in the diagram, they use the exact same amount of material to cover all six faces.

What does the 2 in the formula 2(lw + lh + wh) represent?

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The 2 accounts for opposite faces! A rectangular prism has 6 faces total: 2 faces of size l×w, 2 faces of size l×h, and 2 faces of size w×h.

Do I need to worry about which dimension is length, width, or height?

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No! The surface area formula works regardless of how you label the dimensions. Whether you call them 1×2×3 or 3×2×1, the result is identical.

How can I remember the surface area formula?

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Think "2 of each face type":

  • 2 faces of area l×w
  • 2 faces of area l×h
  • 2 faces of area w×h
Add them up: 2(lw+lh+wh) 2(lw + lh + wh)

What if the orthohedra had different dimensions?

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Then their surface areas would be different! Surface area depends entirely on the actual measurements. Even small changes like 1×2×3 vs 1×2×4 would give different results.

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