The LessonThe 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 CoordinateA 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.