Find the Cuboid Length: Solving Volume = 12X with Height 4cm

Quadratic Equations with Volume Applications

Given the height of the cuboid 4 cm

width of the cuboid is equal to X

length of the cuboid is greater by 2 than its width

The volume of the cuboid is equal to 12X

Calculate the length of the cuboid

444XXX

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Calculate the length of the box
00:03 Use the formula for calculating box volume
00:07 Width times height times length
00:14 Substitute appropriate values and solve for X
00:27 Arrange the equation
00:34 Open parentheses properly, multiply each factor
00:40 Isolate X
01:06 This is the value of X
01:18 Substitute the X value we found to find the box length
01:21 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

Given the height of the cuboid 4 cm

width of the cuboid is equal to X

length of the cuboid is greater by 2 than its width

The volume of the cuboid is equal to 12X

Calculate the length of the cuboid

444XXX

2

Step-by-step solution

To solve this problem, we follow these steps:

  • Step 1: Use the cuboid volume formula Volume=length×width×height\text{Volume} = \text{length} \times \text{width} \times \text{height}.
  • Step 2: Substitute the expressions for length (X+2)(X + 2), width XX, and height 44 into the formula.
  • Step 3: Equate the expression to the given volume 12X12X and solve for XX.
  • Step 4: Once XX is determined, calculate the length as X+2X + 2.

Now, let's work through each step:

Step 1: The formula for volume is:

Volume=length×width×height\text{Volume} = \text{length} \times \text{width} \times \text{height}

Step 2: Substitute the given values:

Volume=(X+2)×X×4=12X\text{Volume} = (X + 2) \times X \times 4 = 12X

Step 3: Solve for XX:

Expanding the left side, we have:

(X2+2X)×4=12X(X^2 + 2X) \times 4 = 12X

This simplifies to:

4X2+8X=12X4X^2 + 8X = 12X

Rearranging gives:

4X2+8X12X=04X^2 + 8X - 12X = 0

4X24X=04X^2 - 4X = 0

Factor out 4X4X:

4X(X1)=04X(X - 1) = 0

Thus, 4X=04X = 0 or X1=0X - 1 = 0. The only meaningful solution (since XX can't be zero) is:

X=1X = 1

Step 4: Calculate the length:

The length is X+2=1+2=3X + 2 = 1 + 2 = 3 cm.

Therefore, the length of the cuboid is 3 cm3 \text{ cm}.

3

Final Answer

3 cm

Key Points to Remember

Essential concepts to master this topic
  • Volume Formula: Length × Width × Height for all cuboids
  • Substitution: Replace variables: (X+2)×X×4=12X(X + 2) \times X \times 4 = 12X
  • Verification: Check dimensions make sense: length 3 > width 1 ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to factor out common terms
    Don't leave 4X24X=04X^2 - 4X = 0 unsolved = missing the factored form! This makes finding X much harder. Always factor out the greatest common factor: 4X(X1)=04X(X - 1) = 0.

Practice Quiz

Test your knowledge with interactive questions

Calculate the volume of the rectangular prism below using the data provided.

888333222

FAQ

Everything you need to know about this question

Why can't X equal zero in this problem?

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If X = 0, then the width would be 0 cm, making it impossible to have a real cuboid! Physical dimensions must be positive numbers.

How do I know which solution to choose?

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Always check if your solutions make physical sense. Since X represents width, it must be positive. That's why X = 1 is correct, not X = 0.

What if I expand the equation wrong?

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Take it step by step: (X+2)×X=X2+2X(X + 2) \times X = X^2 + 2X, then multiply by 4 to get 4X2+8X4X^2 + 8X. Double-check each multiplication!

Why is the length X + 2 instead of just X?

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The problem states the length is greater by 2 than its width. Since width = X, then length = X + 2. Always read the problem carefully!

Can I solve this without factoring?

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You could use the quadratic formula, but factoring is much faster here since 4X(X1)=04X(X - 1) = 0 gives you the solutions immediately!

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