It may be that my references to 'BASIC syntax' might not mean much to some people.
It used to be that every small computer came equipped with BASIC but, as this has not been the case for some years now, I felt it might be useful to give a brief outline of the BASIC syntax you need to use to enter equations for the 'function' command or to create expressions for a program or command.
BASIC is an acronym for Beginners Allpurpose Symbolic Instruction Code and it is the language that most of us over 50 cut our programming teeth on. Over 60 and you were likely to have started programming in binary via a set of switches!
The operators and functions which you can use are listed below. They are all case sensitive.
Package code  Operation 
^  Raise to the power 
*  Multiplication 
/  Fractional, floating point division 
\  Integral division 
mod  Mod, Modulus 
+  Addition or a positive value 
  Subtraction or a negative value 
=  Equality 
>  Greater than * 
<  Less than * 
<>  Not equal to * 
<=  Less than or equal to * 
>=  Greater than or equal to * 
and  Logical AND * † 
or  Logical OR * † 
xor  Logical Exclusive OR, XOR * † 
not  Logical NOT * † ‡ 
eqv  Logical equivalence, Not XOR * † ‡ 
imp  Logical implication * † ‡ 
* The results of logical operations return 1 for True and 0 for False.
†
These operators can be applied to values as well as conditions.
Hover over the reference symbols for examples.
‡ These operators can generate 1's from zeroes. As all of the bits in the number/s are processed, (32 bits in the case of integers), any leading zeroes in the values used will generate 1's and so the result is likely to be a negative number.
Hover over the symbols for examples.
Standard Functions 


Package code  Function 
abs  Abs, the absolute value 
cos  Cos, cosine 
exp  Exp, e^{number}, the antilogarithm 
fix  Fix, = Sgn(number)*Int(Abs(number)) 
int  Int, the integer portion of the number 
log  Log, the natural logarithm 
rnd  Rnd, a random number where 0 £ number < 1 
sgn  Sgn, sign of the number 
sin  Sin, sine 
sqr  Sqr, the positive square root 
tan  Tan, tangent 
Derived Functions 

Package code  Function 
log10  Logarithm to the base 10 
log2  Logarithm to the base 2 
Inverse Trig. Functions 

Package code  Function 
sec  1/Sin, secant 
cosec  1/Cos, cosecant 
cot  1/Tan, cotangent, cotan 
arcsin  'Angle whose sine is' 
arccos  'Angle whose cosine is' 
atn  'Angle whose tangent is', Arctan 
arcsec  'Angle whose secant is' 
arccosec  'Angle whose cosecant is' 
arccot  'Angle whose cotangent is' 
Hyperbolic functions 

Package code  Function 
sinh  Hyperbolic Sine 
cosh  etc. 
tanh  
sech  
cosech  
cotanh  
arcsinh  
arccosh  
arctanh  
arcsech  
arcosech  
arccotanh 
With BASIC, the main rule is that everything has to be stated explicitly. e.g. we all know that 2x means "Two multiplied by x" but this has to be written in full as '2*x' in BASIC.
A second point is that, as all parts of an equation have to be entered in line, far more parentheses are needed than is the case with written algebra. An equation which would usually be written as "1 over 1 + x" has to be entered as 1/(1+x).
Whilst the following is a rule of basic arithmetic not BASIC, a common mistake is to misinterpret expressions such as 2 + 5 x 3 and expect the result '21' when, in fact, it's 17. [21 = (2 + 5) x 3].