Find X in a Parallelogram: Perimeter 10 with Side Length X-2

Parallelogram Perimeter with Variable Side Lengths

Below is a parallelogram.

AB = 4

AC = X-2

The perimeter of the parallelogram is 10.

AAABBBDDDCCC4X-2

Calculate X.

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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 parallelograms
00:11 They are also a pair of opposite sides, therefore equal
00:24 Values of all sides
00:33 The perimeter of the parallelogram equals the sum of its sides
00:48 Let's substitute appropriate values and solve for X
01:02 Group the numbers to one side, and X to one side
01:14 Isolate X
01:25 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

Below is a parallelogram.

AB = 4

AC = X-2

The perimeter of the parallelogram is 10.

AAABBBDDDCCC4X-2

Calculate X.

2

Step-by-step solution

The problem involves calculating X X for a parallelogram with given side lengths and perimeter. Let's proceed step-by-step:

Step 1: First, recognize that in a parallelogram, opposite sides are equal:
- AB=CD=4 AB = CD = 4 (given)
- AC=BD=X2 AC = BD = X-2

Step 2: Use the perimeter formula for the parallelogram:
P=2(a+b) P = 2(a + b)
where a=AB=4 a = AB = 4 and b=AC=X2 b = AC = X-2 .

Step 3: Plug the perimeter value and side lengths into the formula:
10=2(4+(X2)) 10 = 2(4 + (X - 2))

Step 4: Simplify and solve for X X :
10=2(4+X2) 10 = 2(4 + X - 2)
10=2(X+2) 10 = 2(X + 2)

Step 5: Divide both sides by 2 to eliminate the factor:
5=X+2 5 = X + 2

Step 6: Subtract 2 from both sides to isolate X X :
X=3 X = 3

Therefore, the correct value of X X is 3 3 .

The corresponding choice is option 4.

3

Final Answer

3

Key Points to Remember

Essential concepts to master this topic
  • Parallelogram Property: Opposite sides are equal in length
  • Perimeter Formula: P = 2(side₁ + side₂) = 2(4 + (X-2))
  • Check: When X = 3, AC = 1 and perimeter = 2(4 + 1) = 10 ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting opposite sides are equal
    Don't use only AB = 4 and AC = X-2 for the perimeter = AB + AC + ? + ?! This ignores that opposite sides equal each other and gives an incomplete equation. Always remember: perimeter = 2(AB + AC) because CD = AB and BD = AC.

Practice Quiz

Test your knowledge with interactive questions

Find the perimeter of the parallelogram using the data below.

555222

FAQ

Everything you need to know about this question

Why do we multiply by 2 in the perimeter formula?

+

In a parallelogram, opposite sides are equal. So if AB = 4 and AC = X-2, then CD = 4 and BD = X-2 too. The perimeter adds all four sides: 4 + (X-2) + 4 + (X-2) = 2(4 + X-2).

How do I know which sides are opposite?

+

Look at the diagram! In parallelogram ABDC, AB is opposite to CD and AC is opposite to BD. Opposite sides are the ones that don't share a vertex.

What if I get a negative value for X?

+

Check your arithmetic! In this problem, X = 3 is positive. If you get negative, you likely made an error in simplifying or solving the equation.

Can the side length AC actually be negative?

+

No! Side lengths must be positive. Since AC = X-2 and we found X = 3, then AC = 3-2 = 1, which is positive and makes sense geometrically.

How do I check if my answer is correct?

+

Substitute X = 3 back: AB = 4, AC = 3-2 = 1. Perimeter = 2(4 + 1) = 2(5) = 10 ✓. This matches the given perimeter!

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