How to Reflect a Shape in the YAxis Using Cartesian Coordinates
Reflecting a Shape in the YAxis Using Cartesian Coordinates
A shape can be reflected in the yaxis.
If point on a shape is reflected in the yaxis, the ycoordinate stays the same, but the xcoordinate changes sign (becomes negative if it is positive and vice versa).
The image below shows a point on a shape being reflected in the yaxis:

The point A has Cartesian coordinates (3, 4).

The reflected point A' has Cartesian coordinates (−3, 4). The ycoordinate is still 4, but the xcoordinate has changed from 3 to −3.
How to Reflect a Shape in the YAxis Using Cartesian Coordinates
Reflecting a shape in the yaxis using Cartesian coordinates is easy.
Question
Reflect the shape below in the yaxis.
StepbyStep:
1
Find the Cartesian coordinates of each point on the shape.
Write the xcoordinates and ycoordinates of each point.
Point  xcoordinate  ycoordinate 

A  −3  2 
B  −2  5 
C  −1  2 
2
Find the Cartesian coordinates of the reflected points.
Keep the ycoordinate the same, but change the sign of the xcoordinate.
Point  xcoordinate  ycoordinate  Point  xcoordinate  ycoordinate 

A  −3  2  A'  3  2 
B  −2  5  B'  2  5 
C  −1  2  C'  1  2 
3
Plot the reflected points and draw in the shape.
Answer:
We have reflected the shape in the yaxis.
A Formula to Reflect a Point in the YAxis Using Cartesian Coordinates
In general, we write Cartesian coordinates as:
x is the xcoordinate. y is the ycoordinate. x and y can taken any number.
The reflected point has Cartesian coordinates:
The image below shows a general Cartesian coordinate being reflected in the yaxis: