Geometry Everywhere
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Two-link excavator arm

Non-right Triangles: Sine and Cosine Rules

An excavator's arm is just two links: a boom and a stick. When the operator points at a spot, the machine has to know how to get there. But nowhere in that arm is there a right angle, so the right-triangle route is closed. The elbow angle it needs is still pinned to a single value. What pins it?

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