Video explanation
A two-link arm moves a pen: angles yield a position, a path yields joint angles, and the demonstration compares two solutions and unreachable targets.
Forward kinematics
Given link lengths and joint angles, sum trigonometric displacement components to compute the end position.
Multiple inverse solutions
A point may have elbow-up and elbow-down solutions. Continuous drawing needs consistent choices to avoid abrupt joint changes.
Workspace limits
Link lengths and joint limits bound the reachable workspace; points outside it have no feasible solution.