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A tube (hollow cylinder) has an outer radius R and inner radius r. Volume = π(R² − r²) × length. Surface area includes outer surface, inner surface, and the two ring-shaped ends. Used for pipes, ducts, and hollow shafts.

단계별 가이드

1. 1Wall thickness = R − r (outer minus inner radius)
2. 2Cross-sectional area = π(R² − r²)
3. 3Volume = π(R² − r²) × length
4. 4Total SA = 2π(R+r)×length + 2π(R²−r²) (lateral + ends)

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