Trigonometric functions use a certain convention for angles that you may think a little odd. Zero degrees points due east and ninety degrees is due north. If you are using another convention in your game--such as zero degrees due north--then you will have to constantly convert between them when using the trig functions. I advise you not to use another convention in your game. Some things are worth fighting, but not this.
You will need to use Fixed-point numbers with these functions.
fcos(), fsin(), fatan2() and the like are for things that need more than 0 to 360 for angles. Verge defines a constant FIXED_PI, which is approximately the mathematical constant PI * 65536, which is used to measure the angles more accurately since we don't have floats. 2 * FIXED_PI is the same as 360 degrees.