How to reflect shapes on a mirror line
or x axis, y axis, co-ordinate grid, graph or even cartesian plane – it's all pretty much the same.
The biggest problem isn't really the reflection.. it's more making sure that you've correctly identified the ‘mirror line.' This can cause a few problems and a little confusion. The easiest way is to actually plot a couple of points on the graph.
As an example you might be asked to reflect in the line x = 1. In this case find a few co-ordinates that have x equal to 1:
All show the x value at one. Once you've plotted them, join up and you'll get the x = 1 line.
The same is true of y = 4
.. or y = x
Just plotting a few of these co-ordinates will make sure that you always reflect in the correct mirror line.
The only other issue is to make sure that your reflection is at 90 degrees to the line, and it's the same distance both sides. Other than that, you're good to go.
Here's some videos to help: