*Macmillan Science Library: Mathematics*. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.

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## Different Ways to Measure Circles

In degree measure, the circle is divided into 360 equal parts, while in **gradient** measure, 400 equal parts of a circle are used. Since there are four right angles in a circle, there are 100 gradients in a right angle, making gradients a better fit with the decimal system. Nevertheless, degree measure is the predominant system for measuring angles using fractional parts of a circle.

A different method for measuring angles based on a circle is **radian** measure. The importance of radian measure is that numerous results in calculus involving trigonometric functions—for example, **sine**, **cosine**, or tangent—require that the angle of the trigonometric function be measured in radians.

**Using Radian Measure.** To understand radian measure, it is necessary to understand that rather than using the fractional part of a circle cut off by the angle, the fractional part is converted to...

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