I have two objects, A and B, at two different points. I want B to fire at A. B's shot moves so far x and y every frame. How do I get the angle it needs to travel at as two numbers, one representing how much X changes and how much Y changes per frame?
You don't seem to need the angle, only the delta vector between the two positions.
vA = vector representing position of A
vB = vector representing position of B
vD = vA - vB // distance and direction to travel
vD / len(vD) = vDu // direction of travel
And you multiply vDu with your speed per frame, this will give you the distance per frame.
Well, as you mentioned only mathematics tag so I'm assuming that you have to do everything manually, without built-in vectors functionality.
So, I'm writing here on of the may methods to do so.
First find the Slope between two points at which bullet A and B do exist, by which we can calculate angle through which I'll determine the direction.
Slope = m
A's position = x1, y1
B's position = x2, y2
tan inverse = atan
angle = theta
First find m between both bullets as,
m = (y2 - y1)/(x2 - x1)
theta = atan(m)
Now using parametric equation of circle which will give you the direction, and you want B to fire at A
newX = Cos(theta) --(1)
newY = Sin(theta)
B's position = x2 + newX, y2 + newY
Repeat from (1)