After a reflection, pre-image coordinate Y (-3, 2) results in the image coordinate of Y' (2, -3). What is the line of reflection?

1 answer

To find the line of reflection given the pre-image coordinates \( Y (-3, 2) \) and the image coordinates \( Y' (2, -3) \), we can follow these steps:

  1. Find the midpoint of the segment connecting the points \( Y \) and \( Y' \). The midpoint is given by:

    \[ M = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right) \]

    Substituting in the coordinates:

    \[ M = \left( \frac{-3 + 2}{2}, \frac{2 + (-3)}{2} \right) = \left( \frac{-1}{2}, \frac{-1}{2} \right) \]

    So, the midpoint \( M \) is \( \left( -\frac{1}{2}, -\frac{1}{2} \right) \).

  2. Find the slope of the line connecting \( Y \) and \( Y' \). The slope \( m \) is:

    \[ m = \frac{y_2 - y_1}{x_2 - x_1} = \frac{-3 - 2}{2 - (-3)} = \frac{-5}{5} = -1 \]

    The line from \( Y \) to \( Y' \) has a slope of \( -1 \).

  3. Determine the slope of the line of reflection. The line of reflection is perpendicular to the line connecting \( Y \) and \( Y' \). If the slope of the line is \( -1 \), the slope of the line of reflection will be the negative reciprocal:

    \[ m_{reflection} = 1 \]

  4. Use the point-slope form of a line to write the equation of the line of reflection. The point-slope form is:

    \[ y - y_1 = m (x - x_1) \]

    where \( m = 1 \) and \( (x_1, y_1) = \left( -\frac{1}{2}, -\frac{1}{2} \right) \):

    \[ y - \left(-\frac{1}{2}\right) = 1 \left(x - \left(-\frac{1}{2}\right)\right) \]

    Simplifying this gives:

    \[ y + \frac{1}{2} = x + \frac{1}{2} \]

    Rearranging:

    \[ y = x \]

Thus, the line of reflection is given by the equation:

\[ \boxed{y = x} \]