The robotic arm we shall consider here consist of two limb sections, the arm and the forearm, connected at a joint, the elbow. The arm is attached at the other end to the body, and the forearm could connected to a hand. The limbs are connected at their endpoints by joints, shoulder and elbow, that are allowed to rotate in a planar motion.
The problem is to determine the X-Y position of the robotic wrist joint given the angle arm makes with the body, the angle that the forearm makes with the arm, and the length of the limb segments.