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The lines y=x+2  and y=x22  are the tangents of certain circle. If the point (0,2)  lies on the circle then it’s equation is

a
(x−322)2+(y+122)2=94
b
(x+322)2+(y+122)2=94
c
(x−322)2+(y−122)2=94
d
None of the above

detailed solution

Correct option is C

Given lines are y=x+2........(1),y=x−22........(2) Diameter, d=  distance between the two parallel lines (1)&(2)=|c1−c2|a2+b2=|2+22|2=3∴  radius, r=d2=32Let Q be the foot of the perpendicular from P with respect to line (2)h−x1a=k−y1b=−(ax1+by1+c)a2+b2⇒h−01=k−2−1=−(0−2−22)1+1h=k−2−1=322=32∴h=32,k=32+2=−12∴Q(h,k)=(32,−12)∴  Centre =  midpoint of PQ=(32+02,−12+22)=(322,122)∴  Equation of the circle is (x−h)2+(y−k)2=r2⇒(x−322)2+(y−122)2=(32)2⇒(x−322)2+(y−122)2=94

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The locus of the point which moves in a plane so that the sum of the squares of its distances from the lines ax+by+c=0  and bxay+d=0  is r2, is a circle of radius.


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