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## Class 9 math (India)

### Unit 8: Lesson 2

Area of a triangle

# Area of triangle proof

Proof that shows that the area of any triangle is 1/2 b x h. Created by Sal Khan.

## Want to join the conversation?

• The last triangle doesn't make sense to me. Couldyou please explain it to me a diiferent way. I guess that it's finding out the length of the base that I'm having trouble with.

Thanks!

Dallas
(1 vote)
• The length of the base doesn't matter, it is just a line that extends forever. The reason for extending the base is so you can draw a perpendicular line up to the vertex so you can find the height.
• Sal how do you multiply 1/2?That part I didn't get.And I didn't get D c and ABC
• Multiplying by 1/2 is the same as dividing in half or multiplying by 0.5. Remember: multiplying anything below 1 makes the number smaller
(1 vote)
• how do you measure area of the triangle?
• The formula for that is 1/2*b*h, where b is base length and h is height.

Hope this helped.
• why area is very important in our life
• when painting and a bucket of paint paints 16cm and you need to paint 32 cm hom many buckets do you buy
• What does arbitrary mean?
• It mean : based on random choice or personal whim, rather than any reason or system.
Ex: "his mealtimes were entirely arbitrary"
• what is the measure of the height of an Acute triangle
• You just need to find the base then find vertex opposite the base and draw a line from this vertex perpendicular to the base. Finally you just need to measure this height like in right triangle! Hope that is helpfull to you!
• isn't the second triangle a right triangle
• i think there is no point of labelling abc,for the first triangle,we can use a simple way that is divide the area of rectangle by two
(1 vote)
• What is the way you write the formula to find the area of a triangle?