If the line passing through P(1, 2) making an angle π4with the x-axis in the positive direction meets the pair of lines x2+4xy+y2 at A and B, then PA⋅PB=
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a
13/3
b
13/6
c
11/6
d
11/3
answer is A.
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Detailed Solution
x=x1±rcosθ, y=y1±rsinθx=1±r2, y=2±r2 Put 1+r2,2+r2 in x2+4xy+y2=01+r22+2r2+42+2r2+r2+r2+4+r22+4r2=03r2+92r+13=0 is a quadratic equation in r(distance) for which product of the roots (r1r2 or PA.PB ) =133