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How to combat the bothersome incircle construction inaccuracy?

  • 24-05-2012 1:03pm
    #1
    Registered Users Posts: 921 ✭✭✭


    I have trouble constructing a perfect incircle which doesn't go past the three sides of a triangle. Always a part of the circle will jut out and it's an eyesore as i strive to develop a professional representation of my mathematical ability.

    Will I lose many marks? How do you construct a sexy incircle?


Comments

  • Registered Users Posts: 789 ✭✭✭FaoiSin


    You should be able to judge it by eye.


  • Registered Users Posts: 921 ✭✭✭reznov


    Just a little bit always goes astray. :(
    I'm aiming for that Maths certificate and don't want the chief examiner to get the wrong impression.

    I do it by eye! Maybe I need an eye replacement?


  • Closed Accounts Posts: 61 ✭✭cutty9


    you need optilase.

    if you can't get the incircle construction fully exact, i would kill myself reznov.


  • Registered Users Posts: 921 ✭✭✭reznov


    cutty9 wrote: »
    you need optilase.

    if you can't get the incircle construction fully exact, i would kill myself reznov.

    Wait so if I don't get it right, you will kill yourself? A hefty sacrifice indeed comrade.

    Anyone? Any suggestions? Or should I hope for the best as there's no technique?


  • Moderators, Education Moderators Posts: 8,572 Mod ✭✭✭✭Canard


    Draw the circle first, draw a triangle around it, add in the construction lines. ;)


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  • Registered Users Posts: 789 ✭✭✭FaoiSin


    Patchy~ wrote: »
    Draw the circle first, draw a triangle around it, add in the construction lines. ;)

    That's... That's brilliant! :cool:


  • Moderators, Education Moderators Posts: 8,572 Mod ✭✭✭✭Canard


    Works every time, FUQ DA SYSTEM :cool:


  • Registered Users Posts: 921 ✭✭✭reznov


    Patchy~ wrote: »
    Draw the circle first, draw a triangle around it, add in the construction lines. ;)

    If I get the certificate in Maths, I'm dedicating it to YahFaoiSin and you. :cool:


  • Registered Users Posts: 1,763 ✭✭✭finality


    Patchy~ wrote: »
    Draw the circle first, draw a triangle around it, add in the construction lines. ;)

    What if they give you specific measurements for the triangle?


  • Closed Accounts Posts: 4,813 ✭✭✭Togepi


    They usually just give you the triangle don't they?


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  • Moderators, Education Moderators Posts: 8,572 Mod ✭✭✭✭Canard


    I thought that too. I always thought it was kind of accepted the incircles just dont work, my godly JC maths teacher taught us that sneaky trick.

    But I guess youd just make the radius around the length of the side or something like that, might take a few tries but if all else fails just do trial and error or do it the conventional way even if it messes up a bit.


  • Closed Accounts Posts: 3,479 ✭✭✭ChemHickey


    Patchy~ wrote: »
    I thought that too. I always thought it was kind of accepted the incircles just dont work, my godly JC maths teacher taught us that sneaky trick.

    But I guess youd just make the radius around the length of the side or something like that, might take a few tries but if all else fails just do trial and error or do it the conventional way even if it messes up a bit.


    Use your protractor first. then draw the lines after words


  • Registered Users Posts: 1,763 ✭✭✭finality


    I actually don't have trouble with the incircle. Finding the incentre accurately is easy, then just try to sort of line your compass up with the part of the triangle that's closest to the centre, then draw a circle.

    If it's out by like half a millimetre it's not going to be a problem anyway.


  • Registered Users Posts: 1 m4r0s


    assume everyone knows it...but you've to draw a 90 degree line to one of the sides from the incentre, works every time for me


  • Registered Users Posts: 777 ✭✭✭boogle


    m4r0s wrote: »
    assume everyone knows it...but you've to draw a 90 degree line to one of the sides from the incentre, works every time for me
    This


    This is the step that will help accuracy. Once you've found the incentre point, draw a perpendicular line (using the 90 degree edge of your set square) from one side of the triangle to the incentre point. This line is now the radius if your incircle so set your compass to the length of this line, then swing that baby around :)


  • Registered Users Posts: 789 ✭✭✭FaoiSin


    There ya go reznov. A perfect incircle :cool:


  • Moderators, Education Moderators Posts: 8,572 Mod ✭✭✭✭Canard


    It...its beautiful.


  • Closed Accounts Posts: 4,813 ✭✭✭Togepi


    Just make sure your pencil tip is as blunt as possible, therefore you can't but get the circle to touch all three sides! :D


  • Registered Users Posts: 153 ✭✭jos360


    Im did tech graph for JC and was pretty good at it, and they were pretty harsh on docking marks for inaccuracies like those.
    So I found a few ways to make all these constructions pretty god dam perfect :D

    Firstly, when you're bisecting an angle or line, set the length of your compas really long (as in go way outside the triangle). Anyone doing physics, back me up on this one, reduce percentage error FTW!

    Also, sharpen your pencil like crazy for constructions, then snap the top off with you're fingernail so as when you draw the circle, its wider and more likely to touch everywhere you want it to :D

    Last point, if you wanna go hardcore, get a real compass, as in this:
    teaching_supplies_drawing_compass_bow_compass.jpg

    They really help and especially since were allowed plot and measure our co-ordinate geometry questions, being able to measure distances accurately is going to be very important :)


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