\subsection{Inverse Kinematics (IK)}
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Option: Solve Forward Kinematics for angles.\\
Better: Law of cosine with polar coordinates. Compute angle using cosine rule,\\
$\theta_1 = \phi \pm \alpha$, $\theta_2 = \pm(\pi - \beta)$

(Positive for {\color{ForestGreen} Elbow Down}, Negative for {\color{red} Elbow Up})

Extension to 6R:
1. Waist: spherical coords (2 sol.)\\
2. 2 sols from 2R for shoulder + elbow\\
3. Solve for wrist joints (no influence on pos)