Topic explanation

Standard explanation

Inner circle radius r, outer R. Chord of the outer touches the inner at T. Then OT perp the chord and OT=r, so d=r for every such chord.

Key points

• d = inner radius
• same centre
• outer chord tangent to inner
• keep the ideas separate
• The Picture: Inner circle radius r, outer R. Chord of the outer touches the inner at T. Then OT perp the chord an
• WHAT — THE PICTURE: Inner circle radius r, outer R. Chord of the outer touches the inner at T. Then OT perp the chord an
• HOW — Use the idea: Identify what is given, select this topic's rule or evidence, apply it one step at a time, and check
• CORE UNDERSTANDING: Inner circle radius r, outer R. Chord of the outer touches the inner at T. Then OT perp the chord an

Labelled diagram