HP 35s User Manual page 120

Single letter
name
The next equation also obeys the syntax rules. This equation uses the inverse
function, , instead of the fractional form, . Notice that
the SIN function is "nested" inside the INV function. (INV is typed by

Example: Area of a Polygon.
The equation for area of a regular polygon with n sides of length d is:
You can specify this equation as
  
Notice how the operators and functions combine to give the desired equation.
6-18
Entering and Evaluating Equations
Parentheses used to group items
Optional explicit
multiplication
1
n d
Area =
4
d
2 /n
Division is done before
addition
cos( / n )
2
sin( /n)

.)