Video: Naming Rays

Think about rays. Name this ray using symbols. At which point this ray start?

03:10

Video Transcript

Think about rays. Name this ray using symbols. At which point does this ray start?

To help us remember what a ray is in maths, it can be useful to think about where we use the word ray in everyday life. A ray is a type of line that starts from a fixed point and continues infinitely in one direction. In other words, it carries on going. And the everyday example of the word that we can use to help us remember this is the sun’s rays. They start from a fixed point. That’s the sun. They travel in straight lines. And they continue infinitely. In other words, they keep on going.

In the first part of this problem, we are asked to name a ray using symbols. Before we do that, let’s have a look at it and try to understand what’s going on. The fixed point where the ray begins is point B. This is the end of the line. And if we look at the other end of the line, we can see an arrowhead. This means that this is the end of the line that keeps on going. So B must be the start point. The ray also passes through point A. And as we know how rays behave, it doesn’t just stop there. It carries on going. It starts at point B, travels to point A, and continues past point A infinitely on and on and on.

To name the ray using symbols, we need to start with the start point, which is B. We then write the letter for the point that the line travels through, which is A. And to show that this is a ray, we draw an arrow showing the direction of the ray above the two letters. This symbol shows a ray that travels from B through A and onwards.

In our second question, we’re shown another ray. At which point does this ray start? We can see that this particular ray starts at point C. It travels through point D and then continues infinitely on and on and on in the same direction. So the point at which this ray starts is point C. The first ray can be written using symbols BA with an arrow pointing from B to A across the top. This shows that the ray travels from B to A and carries onwards. We can see from the second ray that it starts at point C, continues through point D and onwards. So as we’ve said, the point at which the ray starts is C.

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