Reflection

A reflection is defined by a line called a mirror. Assume the y-axis in the coordinates system to be this mirror line .  In a reflection every point on an object is moved perpendicular to the mirror line so that any segment connecting the corresponding points on the object is bisected by the mirror line.  

For instance, in order to built the reflection of a triangle rectangle defined by the points (1,4),(1,1),(4,1)

 Multiply the x-component  of every point forming the figure by -1

 The graph of this new points gives the figure's reflection 

 Reflection in Islamic Art