How do you figure the trajectory of a bullet in three dimensions? Would you use a math formula like y=mx+b but that would only be 2-d.

Newton''s equations of motion are

x = 1/2 at2 + V0t + x0

where x = (x,y,z) is the position of the bullet
a = (ax,ay,az) is the acceleration caused by any forces acting on the bullet (e.g gravity is (0,9.8,0) m/s2)
v0 = (vx,vy,vz) is the bullets initial velocity and
x0 = (x0,y0,z0