The MATLAB functions sin and cos will be useful. $($sind and cosd if using degrees$).$

The function nargin $($recommended$)$ or the inputParser class $($more powerful but more complex$)$ will be useful.

For string comparison $($figuring out if your unit is 'radians' or 'degrees'$)$ you may like the strcmp $($are two strings$/$character vectors the same?$)$ or strcmpi $($same thing but ignores case$)$ functions, or even the contains function.

For setting up your conditional $($if$)$ statements, you may need a logical operator like && or $||$ and ~$.$