### 11.14.4 The measure of an angle in the plane: angle

See section 12.12.9 for angle measures in three-dimensional
geometry.

The angle command takes three mandatory arguments and one
optional argument. The mandatory arguments are points A,
B and C, which determine an angle BAC. The
optional argument is a string.

angle returns the measure of the angle (in the units that
Xcas is configured for). If there is an
optional fourth argument, the angle will be drawn indicated by a small
arc and labeled with the string. If the angle is a right angle, the
indicator will be a corner rather than an arc.

Input:

angle(0,1,1+i)

Output:

pi/4

Input:

angle(0,1,1+i,"a")

Output:

Input:

angle(0,1,1+i,"")

Output:

Input:

angle(0,1,i,"A")

Output:

Input:

angle(0,1,i,"A")[0]

Output:

pi/2

The angle command has angleat and
angleatraw versions (see section 11.14.1). For
the command line versions of these commands, the optional fourth
argument for angle is replaced by a mandatory fourth argument
for the point to put the measurement.