You'er quite right. Too much math for me.
I did find my mistake though, using my test rig.
(defun c:test2()
(mapcar '(lambda (a / b)
(setq b (print (rtod a)))
(print a)
(print (sin (+ a a)))
(print (equal (sin (+ a a)) 0.0 0.104528)) ; +-3 deg
(print)
)
(mapcar 'dtor '(2 2.9 3 87 87.9 92 92.9 94 176 176.9 177 182 182.9 183 267 267.9 268 272 272.9 273 357 357.9 359))
)
(princ)
)
PS, yes the "Double" got me.