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Question

In the figure below, the rectangle at the corner measures 10cm×20cm. The corner A of the rectangle is also a point on the circumference of the circle. What is the radius of the circle in cm?

103342.jpg

A
10 cm
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B
40 cm
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C
50 cm
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D
30 cm
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Solution

The correct option is C 50 cm
WetakethecornerOofthegivensquareOPQR,containingthe10cm×20cmrectangle,astheorigineandthesidesOP&ORasthecoordinateaxes.LetthesidesofOPQRbe2a.SoOPQRliesinthethirdquadrant.Theinscribecirclesradiusisr=a&centreisC(a,a).ThecirclepassesthroughA(10,20).Theequationofthecircleis(xh)2+(yk)2=r2..........(i)Here(h,k)=(a,a)andr=aequation(i)becomes(xa)2+(ya)2=a2..........(ii)ThecirclepassesthroughA(10,20).i.e(x,y)=(10,20)Soequation(ii)reducesto(10a)2+(20a)2=a2.Onsolvingforaweget|a|=50unitsand10units.(aisalength.Sowedonotconsiderthenegativesign).AlsoA(10,20)lieonthecircle.midwaybetween(a,0)&(0,a).Soa>10units&a>20units.werejecta=10.soa=50unitsAnsOptionC
131788_103342_ans.png

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