Calculate Deltoid Dimensions: Finding DB When AC = 2X and Area = 32 cm²

Area Formulas with Variable Diagonals

Shown below is the deltoid ABCD.

AC = 2X

DB = X

The area of the deltoid is equal to 32 cm².

Calculate DB.

S=32S=32S=322X2X2XXXXAAABBBCCCDDD

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:11 Let's start by calculating the diagonal D to B.
00:15 We'll use the formula for finding a rhombus's area.
00:20 That's diagonal one times diagonal two, divided by two.
00:25 Let's substitute the given values to find diagonal D to B.
00:33 Then, multiply by two to remove the fraction.
00:43 Next, we'll isolate the variable X.
00:56 And that's how we solve this problem!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Shown below is the deltoid ABCD.

AC = 2X

DB = X

The area of the deltoid is equal to 32 cm².

Calculate DB.

S=32S=32S=322X2X2XXXXAAABBBCCCDDD

2

Step-by-step solution

To solve this problem, we will utilize the formula for the area of a deltoid, which is 12×AC×DB \frac{1}{2} \times AC \times DB . Given:

  • Diagonal AC=2X AC = 2X
  • Diagonal DB=X DB = X
  • Area = 32cm2 32 \, \text{cm}^2

The formula for the area of the deltoid is:

Area=12×AC×DB \text{Area} = \frac{1}{2} \times AC \times DB

Substitute the given values into the formula:

32=12×2X×X 32 = \frac{1}{2} \times 2X \times X

Simplify the equation:

32=12×2X2 32 = \frac{1}{2} \times 2X^2

32=X2 32 = X^2

Solve for X X by taking the square root of both sides:

X=32 X = \sqrt{32}

Since DB=X DB = X , the length of diagonal DB DB is 32\sqrt{32} .

Thus, the solution to the problem is 32\sqrt{32}.

3

Final Answer

32 \sqrt{32}

Key Points to Remember

Essential concepts to master this topic
  • Formula: Deltoid area equals half the product of diagonal lengths
  • Technique: Substitute AC = 2X and DB = X into 12×2X×X \frac{1}{2} \times 2X \times X
  • Check: Verify 32×232×12=32 \sqrt{32} \times 2\sqrt{32} \times \frac{1}{2} = 32

Common Mistakes

Avoid these frequent errors
  • Using perimeter formula instead of area formula
    Don't add the diagonal lengths AC + DB = 32! This confuses perimeter with area and gives 2X + X = 32, leading to X = 32/3. Always use Area = (1/2) × diagonal₁ × diagonal₂ for deltoids.

Practice Quiz

Test your knowledge with interactive questions

Indicate the correct answer

The next quadrilateral is:

AAABBBCCCDDD

FAQ

Everything you need to know about this question

What exactly is a deltoid and how is it different from other quadrilaterals?

+

A deltoid (or kite) is a quadrilateral with two pairs of adjacent sides that are equal. Its diagonals are perpendicular, which is why we can use the formula Area = (1/2) × d₁ × d₂.

Why don't we simplify √32 to a decimal?

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The exact answer 32 \sqrt{32} is more precise than a decimal approximation. In mathematics, we often keep answers in radical form unless specifically asked to round.

Can I solve this by setting up the equation differently?

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Yes! You could write 32=12×AC×DB 32 = \frac{1}{2} \times AC \times DB first, then substitute. The key is always using the correct area formula for deltoids.

How do I know which diagonal is which in the diagram?

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Look at the labels carefully! AC connects vertices A and C (vertical diagonal = 2X), while DB connects vertices D and B (horizontal diagonal = X).

What if I got X = ±√32? Should I include the negative?

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Since we're dealing with a length measurement, we only take the positive square root. Distances cannot be negative, so DB = 32 \sqrt{32} cm.

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