ay I have two fixed points F and A, and I move node D (which is connected to A by node J and connected to F by node H and K (review added pictures)), how could I predict how the angles would change?
Is there any way to say how much I need to move my node to get specified angles?
Hope you guys understand, and please let me know if I am unclear.
Just define two vectors which are connected to your point D, $\vec{DH}=\vec{H}-\vec{D}$ and $\vec{DJ}=\vec{J}-\vec{D}$, then take the dot product between the two, divide by the magnitude of both vectors and then take the inverse cosine of the ratio. The result is the angle between the two vectors. After you move D, repeat the process to get the new angles.