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.

❤️ Continue Your Math Journey!

We have hundreds of course questions with personalized recommendations + Account 100% premium

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

Given the parallelogram:

444222AAABBBDDDCCC

Calculate the perimeter of the parallelogram.

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!

🌟 Unlock Your Math Potential

Get unlimited access to all 18 Parallelogram questions, detailed video solutions, and personalized progress tracking.

📹

Unlimited Video Solutions

Step-by-step explanations for every problem

📊

Progress Analytics

Track your mastery across all topics

🚫

Ad-Free Learning

Focus on math without distractions

No credit card required • Cancel anytime

More Questions

Click on any question to see the complete solution with step-by-step explanations