Question

What triangle would be congruent to the original using a reflection over the x axis

Answer 1

Reflection in a Line
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        A reflection over a line k (notation rk) is a transformation in which each point of the original figure (pre-image) has an image that is the same distance from the line of reflection as the original point but is on the opposite side of the line.  Remember that a reflection is a flip.  Under a reflection, the figure does not change size.  

 
The line of reflection is the perpendicular bisector of the segment joining every point and its image.
A line reflection creates a figure that is congruent to the original figure and is called an isometry (a transformation that preserves length).  Since naming (lettering) the figure in a reflection requires changing the order of the letters (such as from clockwise to counterclockwise), a reflection is more specifically called a non-direct or opposite isometry.

      http://www.regentsprep.org/regents/math/geometry/gt1/reflect.htm

Answer 2

Answer: my answer is C

Which triangle would be congruent to the original using a reflection over the x-axis?  Reflect across x-axis mapping rule ( x , y )-->( x,-y )

If the original triangle is A(-3,1)B(-3,5)C(-1,1)

look for the Triangle  

A(-3,-1)

B( -3.-5)

C(-1,-1)