[Astronouth7303]

Remember that in C, those aren't functions or equations. They are statements, executed once.

To assign a function to a variable would be something like:

(type omitted) myfunc = tan;

So you need to declare all three variables, like so:

int tilt_angD = ((((int)TILT_SERVO - 124) * 65)/124));
double tilt_angR = ((tilt_angD *3.14159265)/180.0);
double dist = (80.0/tan(tilt_angR));

Just watch out for integer math.

Just be careful about your floating-point expressions, the RC doesn't like them much.