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 isosceles triangle and vertex angle
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Hi Guys

I have a probably simple problem I need a solution to. I have had a good look on google but to no avail, so any links would be good :)

I have an isosceles, and know the length of all three sides, but no angles. I need to know, in radians, the vertex angle (the angle between the two equal sides).

Anyone know of any links, or solutions to this.

I did have a solution using the right angled triangle on the side of the isosceles triangle, but this doesnt seem to work correctly.

Thanks
Spree

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Quote:
Original post by SpreeTree
I have an isosceles, and know the length of all three sides, but no angles. I need to know, in radians, the vertex angle (the angle between the two equal sides).


Let be

 l the lenght of the equal edges
 b the third edge (the base)
 a the angle between the two equal edges.
 


you know that
      
Sorry for my poor ASCII art!

            ***
          **  *
      l **    * b/2
      **      *
    **a/2-----*
      **      *
        **
           ...

    l * sin(a/2) = b/2


Then
    a = 2*asin(b/(2*l))


And I hope this is not your homework ;)

[Edited by - blizzard999 on January 19, 2005 5:04:31 AM]

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Thanks a lot. Of course now I see what u have done, it makes it pretty obvious, and me pretty simple ;)

And no, its not my homework. I think if it was, I would be the oldest kid in the class ;) Its actually for computing the length of an orbital body so the base of a circle is the same size, regadless of the distance from the centre object...

Thanks
Spree

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All times are ET (US)

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