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

A rectangular prism has a base measuring 5 units by 8 units.

The height of the prism is 12 units.

Calculate its volume.

121212888555

FAQ

Everything you need to know about this question

Why can't X equal zero in this problem?

+

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?

+

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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