HP 35s Scientific Calculator - Manual (Page 79)

Real–Number Functions 4-5
Example:
Show that cosine (5/7) π radians and cosine 128.57° are equal (to four significant
digits).
Programming Note:
Equations using inverse trigonometric functions to determine an angle θ, often look
something like this:
θ
= arctan (y /x).
If x = 0, then y / x is undefined, resulting in the error:   .
Keys: Display: Description:
9
()
Sets Radians mode; RAD
annunciator on.
 
5/7 in decimal format.
     Cos (5/7) π.
9
()

Switches to Degrees mode (no
annunciator).

  Calculates cos 128.57°, which is
the same as cos (5/7)
π.