Calculate AO Length in Kite ABCD: Given Area 42 cm² and Diagonal 14 units

Kite Area Formula with Diagonal Calculations

The kite ABCD shown below has an area of 42 cm².

AB = BC

DC = AD

BD = 14

The diagonals of the kite intersect at point 0.

Calculate the length of side AO.

S=42S=42S=42141414DDDAAABBBCCCOOO

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:16 Let's calculate the length of side AO.
00:19 We'll use the kite area formula.
00:22 It's diagonal one times diagonal two, divided by two.
00:28 Now, substitute the given values to find diagonal AC.
00:49 This gives us the length of diagonal AC.
00:55 Remember, the main diagonal intersects the secondary diagonal.
01:00 And that's how we solve this problem. Great job!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

The kite ABCD shown below has an area of 42 cm².

AB = BC

DC = AD

BD = 14

The diagonals of the kite intersect at point 0.

Calculate the length of side AO.

S=42S=42S=42141414DDDAAABBBCCCOOO

2

Step-by-step solution

We substitute the data we have into the formula for the area of the kite:

S=AC×BD2 S=\frac{AC\times BD}{2}

42=AC×142 42=\frac{AC\times14}{2}

We multiply by 2 to remove the denominator:

14AC=84 14AC=84

Then divide by 14:

AC=6 AC=6

In a rhombus, the main diagonal crosses the second diagonal, therefore:

AO=AC2=62=3 AO=\frac{AC}{2}=\frac{6}{2}=3

3

Final Answer

3 cm

Key Points to Remember

Essential concepts to master this topic
  • Area Formula: For kites use A=d1×d22 A = \frac{d_1 \times d_2}{2} where d₁, d₂ are diagonals
  • Technique: Solve 42=AC×142 42 = \frac{AC \times 14}{2} to get AC = 6
  • Check: Verify AO = AC/2 since diagonals bisect: 6/2 = 3 cm ✓

Common Mistakes

Avoid these frequent errors
  • Using wrong formula or confusing AO with AC
    Don't use AO directly in the area formula = wrong diagonal length! The area formula needs the full diagonal AC, not half of it. Always find the complete diagonal first, then divide by 2 to get AO.

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's the difference between AC and AO in this problem?

+

AC is the full diagonal from vertex A to vertex C, while AO is half the diagonal from vertex A to the center O. Since diagonals bisect each other in kites, AO = AC/2.

Why do we use the area formula with diagonals for kites?

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Kites have perpendicular diagonals that bisect each other, making the area formula A=d1×d22 A = \frac{d_1 \times d_2}{2} perfect for these shapes. It's much easier than breaking into triangles!

How do I know which diagonal is which?

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It doesn't matter! The area formula works with any two perpendicular diagonals. In this problem, BD = 14 is given, and we need to find AC to use the formula.

Can I solve this problem differently?

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Yes! You could split the kite into four right triangles and use their areas, but the diagonal method is much faster and less prone to errors.

What if I got AC = 12 instead of 6?

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Check your algebra! From 42=AC×142 42 = \frac{AC \times 14}{2} , multiply both sides by 2 to get 84=AC×14 84 = AC \times 14 , then divide by 14: AC = 6.

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