12.6.2.1476 FACOS f-a-cos FLOATING EXT
( F: r1 -- r2 ) or
( r1 -- r2 )
r2 is the principal radian angle whose cosine is r1. An ambiguous condition exists if | r1 | is greater than one.
r2 is the principal radian angle whose cosine is r1. An ambiguous condition exists if | r1 | is greater than one.