The length of a chord which is at a distance of 6 cm from the centre of a circle of radius 10 cm is
A
18cm
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B
20cm
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C
12cm
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D
16cm
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Solution
The correct option is D 16cm Given−Oisthecentreofacircleofradius10cm.ABisachordofthegivencircleandABisatadistanceof6cmfromO.Tofindout−ThelengthofAB=?.Solution−WejoinOAanddropaperpendicularONtoAB.ONmeetsABatN.soOAistheradiusofthecircleandOA=10cm.AgainONistheperpendiculardroppedfromOtoABatN.∴ONistheperpendiculardistanceofABfromO.SoON=6cm&∠ONA=90o.∴ΔOANisarighttrianglewithOAashypotenuse.So,applyingPythagorastheorem,wegetAN=√OA2−ON2=√102−62cm=8cm.NowAB=2ANsincetheperpendicular,droppedfromthecentreofacircletoitsanychordbisectsthelatter.∴AB=2×8cm=16cm.Ans−OptionD.