What is a Ray in Geometry? — Definition & Examples
Ray definition in geometry
A ray is part of a line. Rays have a fixed starting point and no end point. A ray extends in only one direction infinitely. The ray's starting point and another point along the ray are used to name the ray in geometry.
Find an LED flashlight. Go into a dark room and turn the flashlight on. You have just modeled a ray, a plane figure in geometry that has one endpoint but continues in the other direction forever. Rays and real-life examples of rays are all around is.
How to draw a ray
To draw a ray, place two points on a piece of paper. Label both points with capital letters. Choose one point to be the endpoint. Use a straightedge to draw a line starting at your endpoint and continuing through your second point. Draw one arrowhead on the open end of your line (the one opposite the endpoint).
Ray symbol and label
To symbolize and label a ray, we need that endpoint identified. We also need some other point along the one-way line. Then, we write the endpoint and other point together as capital letters, capped by a tiny, one-way arrow (pointing to the right), :
This is the symbol for Ray , named after an NFL quarterback, who can throw a football that very nearly moves like a ray. Gravity tugs the football down, but the quarterbacks' arm speed and strength can make short passes look like straight-line rays. He is the endpoint; the traveling football is the one-way line.
Ray in geometry examples
A ray of sunshine is a ray. It originates at our star, the Sun, and travels one way, striking earth some eight minutes after it left its "endpoint," the Sun.
Tennis pro, Rafael Nadal, famously serves tennis balls at some 217 kph (135 mph), which defies gravity's tug so well it seems to travel in a straight line, just like a ray.
The light beam from a classroom LCD projector is a ray; so is light from a movie projector at your local cinema.
The path an arrow travels from a bow is a ray and has the added benefit of being, well, arrow-shaped.
Lasers are excellent examples of rays because unlike sports balls, they are not much affected by earth's gravity, so they shine in steady, straight one-way lines from their source.
A word of caution
Because English-language speakers, readers, and writers move their eyes from left to right, almost all rays you see symbolized in mathematics will have left endpoints and right arrows. Keep in mind, though, geometry is a pure science. Rays can go in any direction, like up, down, left, right, and diagonally.