About the topic "Reflection transformation in geometry"

"Reflection transformation" is one of the four types of transformations in geometry.

Even though students can get this stuff on internet, they do not understand exactly what has been explained. 

To make the students to understand the stuff "Reflection-transformation", we have explained the different rules which we apply to make reflection-transformation.

Rules on finding reflected image

Reflection about the x-axis

Reflection about the y-axis

Reflection about the line y=x

Once students understand the rules which they have to apply for reflection transformation, they can easily make reflection -transformation of a figure.

For example, if we are going to make reflection transformation of the point (2,3) about x-axis, after transformation, the point would be (2,-3). Here the rule we have applied is (x, y) ------> (x, -y). 

So we get (2,3) -------> (2,-3).

Let us consider the following example to have better understanding of reflection.

Question :

Let A ( -2, 1), B (2, 4) and (4, 2) be the three vertices of a triangle. If this triangle is reflected about x-axis, what will be the new vertices A' , B' and C' ?


Step 1 :

First we have to know the correct rule that we have to apply in this problem.

Step 2 :

Here triangle is reflected about x - axis. So the rule that we have to apply here is (x , y) -------> (x , -y)

Step 3 :

Based on the rule given in step 1, we have to find the vertices of the reflected triangle A'B'C'

Step 4 :

(x , y) ----------> (x , -y)

A ( -2, 1 ) ------------ A' ( -2, -1 )

B ( 2, 4 ) ------------ B' ( 2, -4 )

C ( 4, 2 ) ------------ C' ( 4, -2 )

Step 5 :

Vertices of the reflected triangle are                      

                       A' ( -2, -1) , B ( 2, -4 ) and C' ( 4, -2) 

Reflecting over any line

When we look at the above figure, it is very clear that each point of a reflected image A'B'C' is at the same distance from the line of reflection as the corresponding point of the original figure. 

In other words, the line x = -2 (line of reflection) lies directly in the middle between the original figure and its image.

And also, the line x = -2 (line of reflection) is the perpendicular bisector of the segment joining any point to its image. 

Students can keep this idea in mind when they are working with lines of reflections which are neither the x-axis nor the y-axis.

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