Tandy 1000 Basic Reference Manual page 101

Chawter 10 I BASIC Kevwords
ATN Function
ATN(number)
Returns the arctangent of number.
ATN returns the angle (in radians) whose tangent is number.
Number must be given in radians.
BASIC always returns the result as a single precision number
unless you specified the
/D
switch when starting up BASIC.
To convert this value
to
degrees, use ATN(number*PI), where PI
equals 3.141593.
Example
P R I N T
A T N ( 7 )
prints the arctangent of 7 which is 1.428899
X
=
A T N ( Y / 3 )
*
5 7 . 2 9 5 7 8
computes the arctangent of Y13 in degrees and assigns the value
t o
x.
99