# Using Radians

Radians use the idea of a unit circle. One radian is approximately 57.3° and results when the arc length is equal to the radius of the circle. One radian is shown here:

Because the circumference of a circle equals 2∏r, the entire circle (360°) contains 2∏ radians. That means that half a circle (180°) equals ∏ radians. See the picture here:

Radians are often listed with ∏ because that produces an exact answer as opposed to an approximation. We can further divide our unit circle into divisions. For example, if we divide ∏ into thirds, we get the following:

Here it is divided in fourths.

And we could in this same manner divide it as many times as we want.

**Practice:**Match the location on the left with the radian measure on the right.

**Answers:**1) B 2) A 3) F 4) E

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