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### Course: Geometry (all content)>Unit 7

Lesson 9: Advanced area with triangles

# Area of equilateral triangle (advanced)

Sal finds a shaded area defined by two equilateral triangles whose side lengths are given. Created by Sal Khan.

## Want to join the conversation?

• Can there be a video explaining area of a circle not a triangle.
• So I'm doing khan acedmy and it says do a circle inside circle and then I look for videos and it just takes me two triangles
• this dont make no sense
• Where did he get 4 from?!
• i need help for circle in a circle
• do one with a circle in a rectangle
• At , why is the denominator 4 instead of 2? I am still confused here.
• He is calculating the area of the entire equilateral triangle at this point.
The formula for the area of an equilateral triangle is 1/2(base x height)
He has calculated the height as being the square root of 3 divided by 2.
Therefore, Area = 1/2(S x sqr(3)/2), so multiply out the denominators to get (S x sqr(3)) / 4
(1 vote)
• I am trying to use the MS calculator to 45 * ^3, or the algo - 45 * sqrt(button) 3, but I get answer on calc = 135, i watched your calc, 45 * x2 = 77,94 what am I doing wrong? thanks
j
• Six button presses does it on my calculators:

4
5
*
3

=
(1 vote)
• is there another way of doing a rectangle inside a circle