Video: KS1-M19 • Paper 2 • Question 18

Tick the shape that has a line of symmetry.

02:42

Video Transcript

Tick the shape that has a line of symmetry.

We’re given a dotted grid with four shapes on it. There’s a triangle, two four-sided shapes, and a shape that has five sides. We’re asked to tick the shape that has a line of symmetry. What does it mean for a shape to have a line of symmetry? We say that a shape is symmetrical when both sides are the same. So a line of symmetry is like a mirror line down the centre of a shape. Both sides of the line of symmetry or the mirror line are exactly the same.

One way to think about symmetry is to imagining folding one side of the shape across the line of symmetry onto the other side. And as we fold the other side across, we can see that the line of symmetry is exactly in the middle of both sides. And so, eventually, the first side would fall exactly on top of the second side. Both sides of our line of symmetry are exactly the same. So which of our four types has a line of symmetry?

Lines of symmetry don’t just go up and down. So we need to make sure that we look at the shapes from all sorts of different angles. A good idea is to turn our heads and to look at the shape from different positions. Let’s imagine a line that goes up and down or vertically through the middle of each shape. Do any of the shapes have a line of symmetry?

The triangle is not the same on both sides nor is the second shape. Our third shape does have a line of symmetry. Both sides of the line of symmetry are the same. And we could fold the left side across the line. And it would fit exactly on top of the right-hand side. Just to check, the final shape might look like it has a line of symmetry. But it doesn’t. If we were to fold the final shape across the line, it would look something like this. The two sides wouldn’t fit neatly on top of each other.

And so, we know the shape that has a line of symmetry is the third shape. And so, we need to tick this shape. We know it has a line of symmetry because we can draw a line on the shape so that both sides of the line are exactly the same. The third shape has a line of symmetry.

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