Definition: The distance along the curved line making up the
Try this Drag one of the orange dots that define the endpoints of the blue arc.
The arc length will be continuously calculated.
The arc length is the measure of the distance along the curved line making up the
It is longer than the straight line distance between its endpoints (which would be a
There is a shorthand way of writing the length of an arc:
This is read as "The length of the arc AB is 10".
The lower case L in the front is short for 'length'.
However, in many cases the letter L and even the curved line over the AB is left out if there is no doubt about what is meant.
Central angle in degrees
The formula the arc measure is:
Recall that 2πR is the
of the whole circle, so the formula simply reduces this by the
of the arc angle to a full angle (360).
By transposing the above formula, you solve for the radius, central angle, or arc length if you know any two of them.
Central angle in radians*
If the central angle is is
the formula is simpler:
This is the same as the degrees version, but in the degrees case, the 2π/360 converts the degrees to radians.
* Radians are another way of measuring angles instead of degrees. One radian is approximately 57.3°
For more on this see Radians definition.
Other circle topics
Equations of a circle
Angles in a circle
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