Look at your own reflection in a shop window. Your right hand looks like the reflection's left hand, but you are exactly the same distance in front of the glass as your reflection seems to be behind it.

A shape works the same way when we flip it across a line on the co-ordinate plane. What do you think happens to a point's co-ordinates when we flip it across the up-and-down line through the middle?

The new shape we get after a flip is called the image. It is the same size as the first shape but faces the opposite way.

First we look at a triangle flipped in the y-axis. Notice a corner before the flip and its image after. Look at where each corner lands, and how far each corner sits from the mirror line on each side.

Now we look at a different shape, an L-shape, flipped in the x-axis. Notice it before the flip and its image after. Be ready to say which co-ordinate changed and which stayed the same.

Now we plot a reflection together on the board. We will name each image co-ordinate as it lands:

• Plot the triangle at (1, 2), (3, 2), (2, 5).
• First we reflect it in the y-axis and read out each image co-ordinate, checking what happened to the x-co-ordinate.
• Then we take one corner and reflect it in the x-axis instead, to see the other co-ordinate flip.

Now we work through the challenge questions together. Each round asks you to plot a reflected image. As you plot each one, say out loud which axis is the mirror and which co-ordinate flips its sign. On the last round no axis is named: look at the starting point, work out for yourself which axis must be the mirror, say it aloud, then plot the image to check you were right.