Example:

Show that cosine (5/7)π radians and cosine 128.57° are equal (to four significant digits).

Keys:Display:Description:

Ÿ{}



5 7 ‘

)

NzR

.) 

Ÿ{}

.) 

128.57 R

.) 

Programming Note:

 

Sets Radians mode; RAD annunciator on.

5/7 in decimal format. Cos (5/7)π.

Switches to Degrees mode (no annunciator).

Calculates cos 128.57°, which is the same as cos (5/7)π.

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: # & . For a program, then, it would be more reliable to determine θ by a rectangular to polar conversion, which converts (x,y) to (r,θ). See "Coordinate Conversions" later in this chapter.

Real–Number Functions 4–5