Triangle Area with 8-Unit Median-Height: Calculate Using Given Length

Triangle Area with Median-Height Properties

AD is the median and the height of triangle ABC.

AD = 8

Calculate the area of the triangle.

AAABBBCCCDDD58

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:08 Let's calculate the area of triangle ABC.
00:11 AD is the median. It splits the triangle into two parts.
00:16 Using the given data, find the length of BD. Then, figure out DC.
00:21 Remember, the whole side is equal to the sum of BD and DC.
00:26 Put these values into the equation to find BC.
00:30 Now, let's use the formula for the triangle's area.
00:34 It's base times height, divided by two.
00:39 Plug the values into the formula and solve to get the area.
00:53 And that's how we find the solution!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

AD is the median and the height of triangle ABC.

AD = 8

Calculate the area of the triangle.

AAABBBCCCDDD58

2

Step-by-step solution

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

  • Step 1: Identify the given information (height) and determine the relationship with the triangle's base.
  • Step 2: Apply the area formula for triangles using height and base.
  • Step 3: Calculate the area and verify it against plausible solution choices.

Now, let's work through each step:
Step 1: We know that AD=8 AD = 8 is both the median and height. As a midpoint implies BD=DC=BC2 BD = DC = \frac{BC}{2} , set BC=10 BC = 10 ensuring appropriate arithmetic association.
Step 2: Applying the area formula Area=12×BC×AD \text{Area} = \frac{1}{2} \times BC \times AD , substitute BC=10 BC = 10 and AD=8 AD = 8 .
Step 3: Plugging in our values, we get Area=12×10×8=40 \text{Area} = \frac{1}{2} \times 10 \times 8 = 40 .

Therefore, the correct area of triangle ABC \triangle ABC is 40 40 , confirming that choice 2 2 is correct.

3

Final Answer

40

Key Points to Remember

Essential concepts to master this topic
  • Median-Height Rule: When a segment is both median and height, the triangle is isosceles
  • Area Formula: Area = 12×base×height=12×10×8=40 \frac{1}{2} \times \text{base} \times \text{height} = \frac{1}{2} \times 10 \times 8 = 40
  • Verification: Check that D is midpoint of BC and AD ⊥ BC for isosceles triangle ✓

Common Mistakes

Avoid these frequent errors
  • Using wrong base measurement or forgetting the median property
    Don't assume any random base length or ignore that AD is a median = wrong triangle setup! This leads to incorrect area calculations because you're not using the proper isosceles triangle relationship. Always recognize that when a segment is both median and height, the triangle must be isosceles with equal sides.

Practice Quiz

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Can a triangle have a right angle?

FAQ

Everything you need to know about this question

How can one line segment be both a median and a height?

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This only happens in isosceles triangles! When triangle ABC is isosceles with AB = AC, the line from vertex A to the midpoint of base BC is automatically perpendicular to BC, making it both a median and height.

How do I find the base length if it's not given directly?

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From the diagram, you can see that BD = 5, and since D is the midpoint (median property), DC also equals 5. Therefore, BC = BD + DC = 5 + 5 = 10.

Why is the area formula base × height ÷ 2?

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Think of the triangle as half of a rectangle! If you drew a rectangle with the same base and height, the triangle would be exactly half of that rectangle's area.

What if I calculated the area as 20 instead of 40?

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You probably used BD = 5 as the full base instead of BC = 10. Remember: D is the midpoint, so the complete base BC = 2 × BD = 2 × 5 = 10.

How can I check if my answer is reasonable?

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With base = 10 and height = 8, imagine this triangle: it's fairly wide and tall, so an area of 40 square units makes sense. An area of 20 would be too small for these dimensions.

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