Find X in Rectangle: Perimeter 32 with Side Length 2x

Perimeter Formula with Algebraic Expressions

Given the following rectangle:

The perimeter of the rectangle is 32.

Find the value of the parameter x.

AAABBBCCCDDD102x

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find X
00:03 Opposite sides are equal in a rectangle
00:17 The perimeter of the rectangle equals the sum of its sides
00:25 Substitute appropriate values and solve for X
00:53 Collect like terms
01:07 Isolate X
01:23 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 following rectangle:

The perimeter of the rectangle is 32.

Find the value of the parameter x.

AAABBBCCCDDD102x

2

Step-by-step solution

To solve this problem, let's clearly follow these steps:

  • Step 1: Identify the information given and needed for solving.

  • Step 2: Apply the perimeter formula for a rectangle.

  • Step 3: Solve for the unknown variable x x .

Step 1: The rectangle has a perimeter P=32 P = 32 . One pair of opposite sides is 2x 2x and the other pair is 10.

Step 2: The perimeter of a rectangle is calculated by
P=2(l+w) P = 2(l + w) where l l is the length and w w is the width.
Here, l=2x l = 2x and w=10 w = 10 .

Step 3: Substitute the given values into the formula:

32=2(2x+10) 32 = 2(2x + 10)

Expand the equation:

32=4x+20 32 = 4x + 20

To solve for x x , subtract 20 from both sides:

3220=4x 32 - 20 = 4x

12=4x 12 = 4x

Finally, divide both sides by 4 to find x x :

x=124 x = \frac{12}{4}

x=3 x = 3

Therefore, the solution to the problem is x=3 x = 3 .

3

Final Answer

3

Key Points to Remember

Essential concepts to master this topic
  • Perimeter Rule: Rectangle perimeter equals twice the sum of length and width
  • Technique: Substitute known values: 32 = 2(2x + 10)
  • Check: Verify x = 3 gives perimeter: 2(6 + 10) = 32 ✓

Common Mistakes

Avoid these frequent errors
  • Adding instead of multiplying by 2 in perimeter formula
    Don't calculate perimeter as 2x + 10 = 32! This ignores that a rectangle has two pairs of equal sides. The perimeter includes both lengths AND both widths. Always use P = 2(length + width) or P = 2l + 2w.

Practice Quiz

Test your knowledge with interactive questions

Look at the rectangle ABCD below.

Side AB is 6 cm long and side BC is 4 cm long.

What is the area of the rectangle?
666444AAABBBCCCDDD

FAQ

Everything you need to know about this question

Why do we multiply by 2 in the perimeter formula?

+

A rectangle has 4 sides - two lengths and two widths. Since opposite sides are equal, we have 2 × length + 2 × width, which simplifies to 2(l+w) 2(l + w) .

How do I know which measurement is 2x and which is 10?

+

Look at the diagram carefully! The side labeled 2x is the length, and the side labeled 10 is the width. It doesn't matter which you call length or width - just be consistent.

What if I get a negative answer for x?

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Check your algebra! Since x represents part of a side length, it should be positive. A negative x would mean a negative side length, which doesn't make sense for a real rectangle.

Can I solve this equation a different way?

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Yes! You could use P=2l+2w P = 2l + 2w instead: 32 = 2(2x) + 2(10) = 4x + 20. Both methods give the same answer: x = 3.

How do I check if x = 3 is correct?

+

Substitute back: if x = 3, then the sides are 2(3) = 6 and 10. Perimeter = 2(6 + 10) = 2(16) = 32 ✓

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