Answer:
(0, 0)
Explanation:
The given vertices lie on the horizontal line y=8 and the vertical line x=5. The vertices that do not lie on those lines have y=0 and x=0. These are the coordinates of the missing vertex: (x, y) = (0, 0)
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Alternate solution
The diagonals of a rectangle have the same midpoint, so for rectangle ABCD, we have ...
midpoint(AC) = midpoint(BD)
The midpoint of a line segment is the average of its endpoints, so this translates to ...
(A+C)/2 = (B+D)/2
Multiplying by 2 and subtracting B gives ...
A + C = B + D
A + C - B = D
So, we can find the missing vertex by adding the coordinates of the diagonal and subtracting the third vertex:
(0, 8) + (5, 0) - (5, 8) = (0+5-5, 8+0-8) = (0, 0)
The missing vertex is (0, 0).
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Please note that this method works even if the rectangle's sides are not aligned with the axes.