Calculate X: Rectangle Area = 22x with Side Length (x+8)

Quadratic Equations with Factoring Solutions

The area of the rectangle below is equal to 22x x .

Calculate x x .

x+8x+8x+8

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Determine the value of X
00:03 Apply the formula for calculating the area of a rectangle (length x width)
00:13 Substitute in the relevant values according to the given data and proceed to solve for X
00:32 Open the parentheses and multiply 0.5X by the 2 factors
00:57 Arrange the equation so that we have 0 on one side
01:14 Take half X out of the parentheses
01:26 Determine the solution options for X
01:37 X must be greater than 0 given that it's a length of a side
01:40 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

The area of the rectangle below is equal to 22x x .

Calculate x x .

x+8x+8x+8

2

Step-by-step solution

The area of a rectangle is equal to its length multiplied by its width.

Let's write out the known data:

22x=12x×(x+8) 22x=\frac{1}{2}x\times(x+8)

22x=12x2+12x8 22x=\frac{1}{2}x^2+\frac{1}{2}x8

22x=12x2+4x 22x=\frac{1}{2}x^2+4x

0=12x2+4x22x 0=\frac{1}{2}x^2+4x-22x

0=12x218x 0=\frac{1}{2}x^2-18x

0=12x(x36) 0=\frac{1}{2}x(x-36)

For the equation to be balanced, x x needs to be equal to 36.

3

Final Answer

x=36 x=36

Key Points to Remember

Essential concepts to master this topic
  • Rectangle Area Formula: Area equals length times width for all rectangles
  • Factoring Technique: Factor out common term: 12x(x36)=0 \frac{1}{2}x(x-36) = 0
  • Zero Product Check: Verify 12(36)×(36+8)=22(36)=792 \frac{1}{2}(36) \times (36+8) = 22(36) = 792

Common Mistakes

Avoid these frequent errors
  • Forgetting to move all terms to one side before factoring
    Don't leave the equation as 22x=12x2+4x 22x = \frac{1}{2}x^2 + 4x and try to factor! This keeps the quadratic split across both sides. Always move everything to one side first: 0=12x218x 0 = \frac{1}{2}x^2 - 18x , then factor.

Practice Quiz

Test your knowledge with interactive questions

Solve for X:

\( x - 3 + 5 = 8 - 2 \)

FAQ

Everything you need to know about this question

Why does the rectangle have a fractional width of 12x \frac{1}{2}x ?

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Looking at the diagram, one side is labeled as x+8 x+8 (the length), so the other side must be 12x \frac{1}{2}x (the width) to give us the area formula 22x=12x×(x+8) 22x = \frac{1}{2}x \times (x+8) .

Why do we ignore the solution x = 0?

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When we factor 12x(x36)=0 \frac{1}{2}x(x-36) = 0 , we get x = 0 or x = 36. But x = 0 would mean the rectangle has no width, so it wouldn't exist! Only x = 36 makes sense in this context.

How do I know which side is 12x \frac{1}{2}x and which is x+8 x+8 ?

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The diagram shows x+8 x+8 labeled on one side. Since Area = length × width and we're told Area = 22x 22x , the unlabeled side must be 22xx+8 \frac{22x}{x+8} , which simplifies to 12x \frac{1}{2}x when x = 36.

Can I solve this without factoring?

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Yes! You could use the quadratic formula on 12x218x=0 \frac{1}{2}x^2 - 18x = 0 , but factoring is much faster here since we can factor out 12x \frac{1}{2}x immediately.

What if I get a decimal answer instead of 36?

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Double-check your algebra! The most common error is incorrectly distributing 12x×(x+8) \frac{1}{2}x \times (x+8) . Make sure you get 12x2+4x \frac{1}{2}x^2 + 4x , then subtract to get 12x218x=0 \frac{1}{2}x^2 - 18x = 0 .

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