A line of reflection is a line that lies in a position between two identical mirror images so that any point on one image is the same distance from the line as the same point on the other flipped image. Lines of reflection are used in geometry and art classes, as well as in fields such as painting, landscaping and engineering.
Things You'll Need
 Ruler
 Pencil

Plot a point on one image.

Plot a point on the other image on the exact same spot. For instance, if you had two triangles that were mirror images of each other, you could plot a point at the topmost angle of each triangle.

Measure the distance between the two points with a ruler.

Divide the distance measurement by 2 to find the halfway point and mark this point with a small dot.

Repeat the previous steps so that you find at least two more halfway points between the two images.

Use your ruler to draw a straight line connecting all three points that marked halfway spots. If your measurements were correct, this line will be a line of reflection.
References
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