Question
If P and Q are the points of intersection of the circles x2+ y2+ 3x + 7y + 2p – 5 = 0 and x2+ y2+ 2x + 2y – p2 = 0, then there is a circle passing through P, Q and (1, 1) for
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all values of p
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all except one value of p
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all except two values of p
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exactly one value of p
Solution
B.
all except one value of p
Radical axis is x + 5y + p2 + 2p – 5 =0
Equation of circle is
x2 + y2 + 3x + 7y + 2p – 5 + λ [x + 5y + p2 + 2p – 5 ] = 0 …. (i)
(i) passes through (1, 1)