Monday, 11 March 2013

ABCD taken in order is a square B is on X-axis and C is on Y-axis . If the coordinates of A are (12,2) find the coordinates of D.

4 comments:

  1. fantastic !! if u could eloborate the solution might it be useful to many.. Vamsee

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  2. Geometric proof:

    Assuming A,B,C,D taken in the clockwise direction.
    A = (12,2) in first quadrant => D in first quadrant.
    Let C = (0,c) and B = (b,0).

    Now, drop a perpendicular from A to x-axis, call this point E.
    Then, triangles COB and BEA are congurent. O is the origin.
    Thus, OC = BE and AE = OB. => A = (b+c,b).

    (b+c,b) = (12,2) => b = 2, and c = 10.

    D can be found using any of the many properties of a square, e.g. diagonals of a square bisect.
    if D = (x,y) => (x+b,y) = (b+c,b+c). => (x,y) = (c,b+c) = (10,12).

    Curiosity: the center of the square always stays on the line y = x!
    Prashanth.
    PS: Kudos Vamsee!

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