Mid-points of the sides AB and AC of a △ABC are (3, 5) and (-3, -3) respectively, then the length of the side BC is :
A
10
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B
20
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C
15
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D
30
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Solution
The correct option is B20 Given−ABCisatriangle.ThemidpointofACisPandthatofABisQ.tofindout−thelengthofPQ=?Solution−Weshallusethemidpointtheoremwhichsays,thelinejoiningthemidpointsofthetwosidesofatriangle,isparalleltoandhalfthethirdside.∴2PQ=BC.NowP(x1,y1)=(3,5)andQ(x2,y2)=(−3,−3).∴Usingdistanceformula,PQ=√(x1−x2)2+(y1−y2)2=√(3+3)2+(5+3)2units=10units.∴BC=2PQ=2×10units=20units.Ans−OptionB.