Circles
A wheel, a bangle and the full moon all trace the same perfect curve. Chapter 9, Circles, of the NCERT Mathematics textbook for Class 9 studies this curve through its centre, radius, chord, arc and segment. You will prove that equal chords subtend equal angles at the centre, learn how the perpendicular from the centre bisects a chord, and discover the angle properties of cyclic quadrilaterals. Constructions and riders on these theorems build the confidence to argue from a diagram to a proof.
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