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

Test your knowledge with interactive questions

Is the straight line in the figure the height of the triangle?

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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