To find the coordinates of point Y' after reflecting point Y across the line \( y = 1 \), we need to determine the distance of point Y from the line of reflection and then reflect it across that line.
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Identify the coordinates of point Y: \( Y(4, 3) \).
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Calculate the distance from point Y to the line \( y = 1 \): The y-coordinate of Y is 3 and the y-coordinate of the line of reflection is 1. The distance from Y to the line is: \[ 3 - 1 = 2 \]
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Reflect point Y across the line \( y = 1 \): To reflect Y across the line, we subtract the distance from the line: \[ Y' = (4, 1 - 2) = (4, -1) \]
So, the reflected point Y' is at the coordinates \( (4, -1) \).
Therefore, the correct answer is B. Y' (4, -1).