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Question
The lengths of two parallel chords of a circle are 6 cm and 8 cm. If the smaller chord is at distance 4 cm from the centre, what is the distance of the other chord from the centre?
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Solution
Let AB and CD be two parallel chords in a circle centered at O. Join OB and OD.
Distance of smaller chord AB from the centre of the circle = 4 cm
OM = 4 cm
MB = AB/2 = 6/2 = 3cm
In ΔOMB,
OM2 + MB2 = OB2
(4)2 + (3)2 = OB2
16 + 9 = OB2
OB2 = 25
`OB = sqrt25`
OB = 5cm
In ΔOND,
OD = OB = 5cm (Radii of the same circle)
ND = CD/2 = 8/2 = 4cm
ON2 + ND2 = OD2
ON2 + (4)2 = (5)2
ON2 = 25 - 16 = 9
ON = 3
Therefore, the distance of the bigger chord from the centre is 3 cm.
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