Calculate Deltoid Perimeter: Given Area 16cm² with Height 3 and 5 Units

Deltoid Geometry with Diagonal Bisection Properties

What is its perimeter of the deltoid ABCD if its area is 16cm²?

333555AAABBBCCCDDDEEE

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:06 Let's calculate the perimeter of the kite together.
00:09 We'll use the kite's area formula to find diagonal D B.
00:13 It's diagonal times diagonal, then divide by 2.
00:17 Remember, the whole side equals the sum of its parts.
00:21 We'll plug in the values we know to solve for D B.
00:29 First, divide 8 by 2.
00:32 Next, let's focus on finding D B.
00:36 Great! This gives us the length of diagonal D B.
00:41 In a kite, the main diagonal crosses the secondary one at right angles.
00:49 Remember, the diagonals of a kite are perpendicular.
00:53 Now, we'll use the Pythagorean theorem in triangle A E D.
00:58 We'll substitute the values to find the length of A D.
01:13 Great job! This is the length of side A D.
01:17 In a kite, remember adjacent sides are equal.
01:24 Now let's apply the Pythagorean theorem in triangle C E D.
01:30 By substituting values, we'll find the length of D C.
01:47 Great! This is the length of D C.
01:50 Remember, adjacent sides in a kite are equal.
01:57 To find the kite's perimeter, add up all the side lengths.
02:05 And that's how we solve this problem! Well done!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

What is its perimeter of the deltoid ABCD if its area is 16cm²?

333555AAABBBCCCDDDEEE

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Step 1: Calculate the full length of diagonal BDBD using the area formula.

  • Step 2: Use the Pythagorean theorem to find the side lengths of the deltoid.

  • Step 3: Calculate the perimeter by summing all the side lengths.

Let's work through the solution:

Step 1: The area formula for a deltoid/kite with diagonals d1d_1 and d2d_2 is: Area=12×d1×d2 Area = \frac{1}{2} \times d_1 \times d_2 Given that d1=AE+EC=3+5=8d_1 = AE + EC = 3 + 5 = 8 cm, we can solve for d2=BDd_2 = BD.

Since the area is 16 cm2^2, substitute the values: 16=12×8×BD 16 = \frac{1}{2} \times 8 \times BD BD=4cm BD = 4 \, \text{cm}

Step 2: The frame of the deltoid breaks into two congruent right triangles due to symmetry.
Let's consider triangle ABEABE: - AE=3AE = 3 cm and BE=BD/2=2BE = BD/2 = 2 cm (as BDBD bisects ACAC).
- Using the Pythagorean theorem: AB2=AE2+BE2=32+22=9+4=13 AB^2 = AE^2 + BE^2 = 3^2 + 2^2 = 9 + 4 = 13 AB=13 cm AB = \sqrt{13} \text{ cm}

For triangle CEDCED:
- CE=5CE = 5 cm and again DE=2DE = 2 cm.
- Therefore, for side CDCD: CD2=CE2+DE2=52+22=25+4=29 CD^2 = CE^2 + DE^2 = 5^2 + 2^2 = 25 + 4 = 29 CD=29 cm CD = \sqrt{29} \text{ cm}

Step 3: The deltoid ABCD is symmetric, thus AB=CDAB = CD and BC=ADBC = AD, so: Perimeter=2AB+2CD=213+229cm \text{Perimeter} = 2AB + 2CD = 2\sqrt{13} + 2\sqrt{29} \, \text{cm}

Therefore, the perimeter of the deltoid ABCD is 213+2292\sqrt{13}+2\sqrt{29} cm.

3

Final Answer

213+229 2\sqrt{13}+2\sqrt{29} cm

Key Points to Remember

Essential concepts to master this topic
  • Area Formula: For kites/deltoids use Area = 12×d1×d2 \frac{1}{2} \times d_1 \times d_2
  • Pythagorean Method: Find side lengths using AB2=AE2+BE2=32+22=13 AB^2 = AE^2 + BE^2 = 3^2 + 2^2 = 13
  • Symmetry Check: Verify opposite sides are equal: AB = DC and AD = BC ✓

Common Mistakes

Avoid these frequent errors
  • Using wrong diagonal lengths in area calculation
    Don't use just the given segments 3 and 5 as full diagonals = wrong area formula! These are half-lengths from center to vertices. Always add segments to get full diagonal lengths: AC = 3 + 5 = 8 cm.

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

Why do the diagonals of a deltoid intersect at right angles?

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In deltoids (kites), the diagonals are perpendicular because of the symmetry property. This creates right triangles that we can solve using the Pythagorean theorem.

How do I know which segments to add for the full diagonal?

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Look at the diagram carefully! The diagonal AC goes from vertex A through center E to vertex C. So AC = AE + EC = 3 + 5 = 8 cm.

Why is the diagonal BD only 4 cm when the other is 8 cm?

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This comes from the area formula! Since Area = 16 cm² and AC = 8 cm, we solve: 16=12×8×BD 16 = \frac{1}{2} \times 8 \times BD , giving BD = 4 cm.

Can I use the distance formula instead of Pythagorean theorem?

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Yes, but the Pythagorean theorem is simpler here! Since we have right triangles with known leg lengths, c2=a2+b2 c^2 = a^2 + b^2 is the most direct approach.

How do I remember which sides are equal in a deltoid?

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Deltoids have two pairs of adjacent equal sides. From the symmetry, AB = AD and CB = CD. The perimeter is 2AB + 2CD or equivalently 2AD + 2CB.

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