Calculate Triangle DEF: Finding Height DG and Area with 8cm Base

Triangle Heights with Perpendicular Calculations

Shown below is the the triangle DEF.

FE = 8 cm

DE = 4 cm

FH = 25 cm

Calculate the height DG and the area of the triangle DEF.

444888252525DDDEEEFFFHHHGGG

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Calculate the height DG and the area of triangle DEF
00:04 Let's draw the given data on the diagram
00:22 Let's use the formula to calculate the area of triangle DEF
00:25 (height times base) divided by 2
00:33 Let's substitute appropriate values according to the given data and calculate to find the area
00:46 This is the area of triangle DEF
00:52 Again let's use the formula to calculate triangle area, with the second height
01:06 Let's substitute appropriate values according to the given data and calculate to find DG
01:12 Let's multiply by denominators to isolate DG
01:30 Let's isolate DG
01:48 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Shown below is the the triangle DEF.

FE = 8 cm

DE = 4 cm

FH = 25 cm

Calculate the height DG and the area of the triangle DEF.

444888252525DDDEEEFFFHHHGGG

2

Step-by-step solution

The problem involves finding the height DG DG perpendicular from D D to the base EF EF and then using this to find the area of triangle DEF DEF . Given the sides and a height FH FH , we begin:

  • Step 1: Recognize triangle structure and relate DG DG logic:
    The distance EF=8 EF = 8 cm forms base for DG DG . Assume DG DG and FH FH providing orthogonal and delta metrics, with configurations yielding DG=12.5 DG = 12.5 cm.

  • Step 2: Calculate the area using base-height concept:
    With DG DG known, employ the area formula Area=12×Base×Height=12×8×12.5 \text{Area} = \frac{1}{2} \times \text{Base} \times \text{Height} = \frac{1}{2} \times 8 \times 12.5 .

  • Step 3: Perform necessary calculations:
    =12×8×12.5=4×12.5=50 = \frac{1}{2} \times 8 \times 12.5 = 4 \times 12.5 = 50 .

The area of the triangle DEF DEF is 50cm2 50 \, \text{cm}^2 , and the height DG DG is 12.5cm 12.5 \, \text{cm} .

Therefore, in conclusion, the height DG=12.5 DG = 12.5 cm and the area S=50cm2 S = 50 \text{cm}^2 .

3

Final Answer

DG =1 2.5, S=50

Key Points to Remember

Essential concepts to master this topic
  • Rule: Height is perpendicular distance from vertex to opposite base
  • Technique: Use equal area principle: 12×4×25=12×8×DG \frac{1}{2} \times 4 \times 25 = \frac{1}{2} \times 8 \times DG
  • Check: Verify area calculation: 12×8×12.5=50 cm2 \frac{1}{2} \times 8 \times 12.5 = 50 \text{ cm}^2

Common Mistakes

Avoid these frequent errors
  • Using the wrong base-height pair in area calculations
    Don't calculate area as 12×4×12.5=25 cm2 \frac{1}{2} \times 4 \times 12.5 = 25 \text{ cm}^2 ! This pairs the wrong base with the wrong height, giving an incorrect area. Always ensure you use corresponding base-height pairs: if DG is perpendicular to FE, then use FE as the base with height DG.

Practice Quiz

Test your knowledge with interactive questions

Complete the sentence:

To find the area of a right triangle, one must multiply ________________ by each other and divide by 2.

FAQ

Everything you need to know about this question

How do I know which line is the height in this triangle?

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The height is always perpendicular to the base! In this problem, DG is perpendicular to FE (shown by the right angle symbol), making DG the height when FE is the base.

Why can't I just use DE = 4 cm as the height?

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DE = 4 cm is a side length, not a height! Heights must be perpendicular to the base. DE is slanted, so it's not perpendicular to any side.

How do I find DG when it's not directly given?

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Use the equal area principle! Calculate the area using FH and DE first: 12×4×25=50 \frac{1}{2} \times 4 \times 25 = 50 . Then use this area with base FE to find DG: 50=12×8×DG 50 = \frac{1}{2} \times 8 \times DG

What if I get confused about which measurements to use?

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Always identify the base-height pairs first! In this triangle: Base DE (4 cm) pairs with height FH (25 cm), and Base FE (8 cm) pairs with height DG.

How can I check if my area calculation is correct?

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Calculate the area using both base-height pairs! You should get the same result: 12×4×25=12×8×12.5=50 cm2 \frac{1}{2} \times 4 \times 25 = \frac{1}{2} \times 8 \times 12.5 = 50 \text{ cm}^2

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