AB and AC are two chords of a circle of radius r such that AB = 2AC. If p and q are the distances of AB and AC from the centre. Prove that -Maths 9th

1 Answer

Answer :

Draw OM perpendicular AB and ON perpendicular AC Join OA. In right △OAM, OA2  = OM2   + AM2   ⇒ r2 = p2 + (1/2AB)2   (Since,OM perpendicular AB,   ∴ OM bisects AB ) ⇒ 1/4AB2  = r2 - p2  or  AB2  = 4r2  - 4p2  ...(i) In right  △OAN, OA2  = ON2 + AN2  ⇒ r2 = q2 + (1/2AC)2    (Since ON perpendicular AC,  ∴ ON bisects AC ) ⇒  1/4AC2  = r2 - q2  or 1/4(1/2AB)2 = r2 - q2 (Since AB = 2AC) ⇒ 1/16AB2 = r2 - q2  or  AB2 = 16r2 - 16q2   ....(iii) From (i) and (ii), we have  4r2 - 4p2 = 16r2 - 16q2 or  r2 - p2  = 4r2 - 4q2 or 4q2 = 3r2 + p2

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