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TEAS MathematicsRadius drives everything

CirclesATI TEAS 7 cheat sheet

Radius drives everything

9 key facts Reviewed Oct 2026
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Parts

  • Radius — center to edge
  • Diameter — edge to edge through the center, = 2r
  • Chord — any segment joining two points on the circle

Formulas

  • C = 2πr
  • A = πr²
  • π ≈ 3.14 (or 22/7)

The Common Error

  • Given the diameter, halve it before using A = πr²
  • A 10 cm circle usually means d = 10, so r = 5

Arcs & Sectors

  • A fraction of the circle: (angle/360) × C or × A
Key takeaway

Radius drives everything

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