Equation of a circle through the origin and belonging to the co-axial system, of which the limiting points are (1,2),(4,3) is
A
x2+y2−2x+4y=0
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B
x2+y2−8x−6y=0
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C
2x2+2y2−x−7y=0
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D
x2+y2−6x−10y=0
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Solution
The correct option is D2x2+2y2−x−7y=0 Since the limiting points of a system of coaxial circles are the point circles (radius being zero), two members of the system are (x−1)2+(y−2)2=0⇒x2+y2−2x−4y+5=0 and (x−4)2+(y−3)2=0⇒x2+y2−8x−6y+25=0 The co-axial system of circles with these as members is x2+y2−2x−4y+5+λ(x2+y2−8x−6y+25)=0 It passes through the origin if 5+25λ=0 or λ=−(1/5), which gives the equation of the required circle as 5(x2+y2−2x−4y+5)−(x2+y2−8x6y+25)=0 ⇒4x2+4y2−2x−14y=0⇒2x2+2y2−x−7y=0