In the figure, segAB and segAD are the chords of the circle. C is a point on the tangent of the circle at point A. If m(arcAPB)=800 and ∠BAD=300, m∠BAC in degree is
A
60
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B
50
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C
40
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D
30
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Solution
The correct option is C 40 Given−OisthecentreofacirclewithatangentACatA.AB&ADaretwochords.m(arcAPB)=60oand∠BAD=30o.Tofindout−∠BAC=?.Solution−WejoinAO,BOandBD.Nowm(arcAPB)=80omeans∠AOB=80o.Weknowthattheangle,subtendedbyachordofacircleatthecentre,isdoubletheanglesubtendedbythesamechordatthecircumferenceofthecircle.∴∠ADB=12×∠AOB=12×80o=40o.Againweknowthattheangle,betweenatangenttoacircleandthechordatthepointofcontact,isequaltotheanglesubtendedbythesamechordinthealternatesegmentofthecircle.∴∠BAC=∠ADB=40o.Ans−OptionC.