## The Lesson

The radial coordinate is the first number in the pair of numbers used to describe polar coordinates. For example, in the polar coordinates (5, 45°), the radial coordinate is 5 (the number on the left): The radial coordinate is sometimes called the radius.

## What Does the Radial Coordinate Mean?

The radial coordinate tells you how far a point is from the pole. If a point has polar coordinates (5, 45°), the point would be 5 from the pole. The image below shows what we mean by a point being 5 units from the pole: ## Using a Polar Grid to Find the Radial Coordinate

A polar grid can be used to find the radial coordinate. A polar grid is shown below: A circle is shown in red. If we read along the horizontal axis (called the polar axis), we see that this circle is labelled 5. This circle has a radius of 5. All points on it have a radial coordinate of 5.

## The Radial Coordinate Can Only Be Positive

The radial coordinate can only be a positive numbers (0, 1, 2, 3...). It does not matter which direction a point is from a point, the distance is positive. 