This page explains how to define a function.
Defining functions is just as easy as variables. It starts with a name followed by list of parameters in parentheses followed by the = sign. For example, you could type:
my_func(x,y)=x+y^2
Alternatively you could do this is by including the function in the math expression as you like. For example if you type:
100+interestOf(100,0.05)
Then press ENTER. Smart Math Calculator would then automatically add interestOf(x,y) functions and await your implementation of this function:
Here are some more examples of defining functions: