In Figure, A, B, C and D are four points on a circle. AC and BD intersect at a point E such that ∠BEC=130oand∠ECD=20o. Then ∠BAC is
A
140o.
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B
110o.
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C
70o.
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D
120o.
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Solution
The correct option is C110o. Given−A,B,C&Darepointsonthecircumferenceofacircle.AC&BDintersectatE.AB&CDhavebeenjoined.∠BEC=130o&∠ECD=20o.Tofindout−∠BAC=?Solution−WejoinBC.∠DEC+∠BEC=180o.(linearpair)∴∠DEC=180o−∠BEC=180o−130o=50o.So,inΔDEC,wehave∠CDE=180o−(∠DEC+∠ECD)=180o−(50o+20o)=110o.(anglesumpropertyoftriangles)NowthechordBCsubtends∠CDE&∠BACtothecircumferenceofthegivencircleatD&Arespectively.∴∠CDE=∠BAC=angle(sincetheangles,subtendedbyachordofacircletodifferentpointsofthecircumfereceofthesamecircle,areequal).Ans−OptionB.