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

Question

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

333555AAABBBCCCDDDEEE

Video Solution

Solution Steps

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 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.

Answer

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