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with only have the points on a triangle how would you determine the radius and center of the incircle of that triangle?

  • math -

    There are 4 centres of a triangle,
    the centroid, the orthocentre, the circumcentre and the incentre.

    of those four you asked for the hardest one to find, lol

    By definition, the incentre is the point in a triangle which is equidistant from each of the three sides

    Are you familiar with the formula for finding the distance from a given point to a given line?

    The distance from (p,q) to the line Ax + By + C = 0
    = |Ap +Bq + C|/√(A^2+B^2)

    so find the equation of each of the 3 sides of the triangle and write them in the general form
    Ax+By+C=0
    then using your given point, find 3 different expressions for the distance.
    They must all be equal.
    form 2 equations by setting any two of the expressions equal to each other.
    That will give you 2 equations containing p and q.
    solve.
    Good luck, this is usually a very messy problem unless it was carefully planned.

    (If somebody has a better way to do this, I would appreciate letting me know)

  • math -

    The general form of the equations are (4/3)x+y=(1688/3)
    (-9/40)x+y=(19577/40)
    (5/12)x+y=(-3929/12)
    but then when I use the incenter(p,q)and express it for distance and set the equations equal to each other i get different things when I set the first 2 equations together than I do the second 2 and the first and last. Can you tell me what I am doing wrong?

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