Results 1 to 9 of 9

Thread: Math Help Needed!

  1. #1

    Math Help Needed!

    OK geniuses...I have an equilateral triangle that is 20" from point to point to point. If I draw a circle that hits all three points, what's the diameter of the circle?
    If I spent some time online looking for the formulas, I might be able to figure this out, but I know you guys are geniuses, so, solve for X, please.
    Oh...I have an upright compressor with 3 feet. I want to put it on a square pad and need to know what dimensions to make the square.
    Last edited by Derek Arita; 06-17-2019 at 3:57 PM.

  2. #2
    Join Date
    Oct 2014
    Location
    Pittsburgh, PA
    Posts
    45
    The term you're looking for is "circumscribed". See here for an explanation. In the case of an equilateral triangle, the radius = side/square root(3). In your case, that would be 11.547. Closest reasonable fraction would be 11 17/32. (35/64 will get you closer, though I've always found measuring anything less than 32nds to be a waste of time).
    Last edited by Patrick Varley; 06-17-2019 at 4:07 PM.

  3. #3
    See...I knew someone here would have it. So, with a radius of 11.547", the diameter would be approximately 23". If I make a square pad of 23" x 23", I should be good. Thanks so much, Patrick!

  4. #4
    Join Date
    Feb 2008
    Location
    E TN, near Knoxville
    Posts
    8,058
    Quote Originally Posted by Derek Arita View Post
    See...I knew someone here would have it. So, with a radius of 11.547", the diameter would be approximately 23". If I make a square pad of 23" x 23", I should be good. Thanks so much, Patrick!
    As usual, someone programed a calculator for this and put it on a web page: https://keisan.casio.com/exec/system/1223429573

    Another way to figure your pad size is do draw the triangle on a big piece of paper, poster board, plywood, or floor. Then measure to see what size of pad makes sense based perhaps on the material and how much extra space you want outside the air compressor feet. Or pretend centimeters are inches and draw it out on a smaller piece of paper.

    JKJ

  5. #5
    Quote Originally Posted by John K Jordan View Post
    As usual, someone programed a calculator for this and put it on a web page: https://keisan.casio.com/exec/system/1223429573

    Another way to figure your pad size is do draw the triangle on a big piece of paper, poster board, plywood, or floor. Then measure to see what size of pad makes sense based perhaps on the material and how much extra space you want outside the air compressor feet. Or pretend centimeters are inches and draw it out on a smaller piece of paper.

    JKJ
    John, what another great idea! I never thought of that. Thank you.

  6. #6
    Join Date
    Feb 2013
    Location
    Tippecanoe County, IN
    Posts
    467
    Yes, that triangle will fit a 23.1" circle. But it will also fit a 19.32" square. (20" times cos(15))

    01bdac389889a5fe7e7c874e808cf86ed4ce834cc3.jpg
    Last edited by David L Morse; 06-17-2019 at 6:48 PM.
    Beranek's Law:

    It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
    L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.

  7. #7
    I'd bisect each of the 60 degree angles and draw lines from the point to the intersection of the 3 angles. From the intersection measure to the outside or let your compass do the walking.

  8. #8
    Join Date
    Apr 2017
    Location
    Tucson, Arizona
    Posts
    208
    Quote Originally Posted by Derek Arita View Post
    OK geniuses...I have an equilateral triangle that is 20" from point to point to point. If I draw a circle that hits all three points, what's the diameter of the circle?
    If I spent some time online looking for the formulas, I might be able to figure this out, but I know you guys are geniuses, so, solve for X, please.
    Oh...I have an upright compressor with 3 feet. I want to put it on a square pad and need to know what dimensions to make the square.
    Hi Derek,
    Here is a "simple" formula that will work for any equilateral triangle inscribed in a circle. So you can use this to calculate the circle diameter for any size equilateral triangle.
    David

    Equilateral Triangle Inscribed in Circle.jpg Triangle in Circle.pdf

  9. #9
    Thanks David and thanks all for the help. I just couldn't get my mind to go there, but I knew you guys could.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •