Bullets directional path

You're going to have to give them a direction vector eventually. Given that polar coordinates (angle and distance) are converted to cartesian coordinates (x and y) using sine and cosine, I expect most people are going to say yes. Those same transforms also work for 3 dimensions.

so what happens with the z axis for sinf and cosf? , if they are only for x,y

If your programming language has a vector class or set of functions, you don't need to do the trig.

Given a vector for the base_position_vector of the ship and a unit vector in the direction the ship is heading when the bullet is fired, the bullet's location is:

base_position_vector + speed*time*direction_unit_vector

If you need more specific information, you'll have to be more specific about your needs.

There is a 3-d equivalent to 2-d polar coordinates - spherical coordinates - that uses two angles instead of just one and can specify any direction in 3-d. However, as Buckeye said, if you have a forward direction vector for your ship, you already have all the information you need, so there's really no reason to use trig for this. (And if you're *rendering* your ship, which you presumably would be, then somewhere you must have a transform for it, in which case you have the forward direction vector.)