Two reflections is a translation or a rotation

The blue triangle is reflected across the purple line to produce the purple triangle. Then the purple triangle is reflected across the red line to produce the red triangle.[br][br]When the two lines are parallel the red triangle is a translation of the blue triangle. When the lines intersect with an angle [math]\theta,[/math] the red triangle is the rotation of the blue triangle by an angle [math]2\theta[/math] about the point of intersection.
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Information: Two reflections is a translation or a rotation