Answer:
(-1, -3)
Explanation:
We suppose your notation means you want to reflect given point P across the horizontal line y=1.
The x-coordinate will remain the same.
The new y-coordinate will be such that y=1 is the midpoint between the original and its reflection:
(5 + y)/2 = 1
5 + y = 2 . . . . multiply by 2
y = 2 -5 = -3 . . . subtract 5
The reflected point is (-1, -3).
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The same sort of math applies whenever you have a midpoint and want to find the other end point. Double the midpoint value and subtract the end point you have in order to find the other end point.