Show that the points A(0,6), B(2,1) and C(7,3) are the three corners of a square ABCD. Find i) the slope of the diagonal BD and ii) the coordinates of the fourth vertex D.

Let the coordinates of the fourth vertex D be (x,y).


Mid point of diagonal AC=0+72,6+32=72,92Mid point of diagonal BD=2+x2,1+y2We know that, diagonals of square bisect each other. So, Mid point of diagonal AC=Mid point of diagonal BD72,92=2+x2,1+y22+x2=72    and    1+y2=92x=5  and y=8Now,Slope of diagonal BD=1-82-5=73             Using formula, m=y2-y1x2-x1And, the coordinates of fourth vertex D=5,8

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