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@@ -9,13 +9,14 @@ A **vector** here is nothing mystical: a pair of numbers `(x, y)`. We use the
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same value to mean two different things depending on context:
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- a **position** — a point in the world.
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- a **displacement / velocity** — an arrow: "move this much in x, this much in y."
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- a **displacement / velocity** — an arrow: "move this much in x, this much in
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y."
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That's it. All of 2D physics is built on adding, subtracting, and scaling these
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pairs.
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- `add(a, b)` → `(a.x + b.x, a.y + b.y)` — apply an arrow to a point.
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- `sub(a, b)` → `(a.x - b.x, a.y - b.y)` — the arrow that points *from b to a*.
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- `sub(a, b)` → `(a.x - b.x, a.y - b.y)` — the arrow that points _from b to a_.
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- `scale(a, s)` → `(a.x * s, a.y * s)` — make an arrow longer/shorter.
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> Note: we return **new** objects (pure functions) here for clarity. Your real
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