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To ensure that UA¯¯¯¯¯⊥AD¯¯¯¯¯, the slope of UA must be the negative reciprocal of the slope of AD.
First, find the slope of UA:
Slope of UA = (10-10)/(5-15) = 0
Since the slope of UA is 0, the negative reciprocal will be undefined.
This means that AD must be a vertical line. The x-coordinate of D must be 15 to be vertically aligned with the x-coordinate of A.
Therefore, the coordinates of point D are (15, y). To determine y, we know that UD must be perpendicular to UA, which is a horizontal line.
Therefore, y = 10
So, the coordinates of point D are (15, 10), which corresponds to answer choice b. (15, 0).