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`"AA" = 2 * tan^-1( sqrt(((s- "b" )(s- "c" ))/(s*(s- "a" )))) _(where) "s" = ( "a" + "b" + "c" )/2`

Enter a value for all fields

The **Triangle Angle** calculator computes the interior angle (AA) of a triangle given the length of the three sides (a, b & c).

**INSTRUCTIONS:** Choose units and enter the following:

- (
**a**) the length of side a - (
**b**) the length of side b - (
**c**) the length of side c

**Triangle Angle (AA):** The calculator returns the angle in degrees. However, this can be automatically converted to other angle units (e.g. radians) via the pull-down menu.

This is derived from the following equation:

`tan("AA"/2) = sqrt( ((s-b)(s-c)) / (s*(s-a)) )` where the semi-perimeter: `s = (a + b + c)/2`

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- Light and Matter(Dr. Benjamin Crowell) Chapter 0.12 Summary