The circumcircle of the triangle whose sides are L1=3x+y−5=0,L2=2x+y−3=0,L3=3x+2y−7=0 is
A
x2+y2−21x+7y−40=0
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B
x2+y2+21x−7y−40=0
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C
x2+y2+21x+7y−40=0
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D
x2+y2+21x+7y+40=0
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Solution
The correct option is Cx2+y2+21x+7y−40=0 The desired circle is αL2L3+βL3L1+γL1L2=0 ⇒α(2x+y−3)(3x+2y−7)+β(3x+2y−7)(3x+y−5)+γ(3x+y−5)(2x+y−3)=0 ...................(1) coeff.x2=coeff.y2 ⇒6α+9β+6γ=2α+2β+γ ∴4α+7β+5γ=0 (on transposing from RHS to LHS) Coeff.xy=0⇒7α+9β+5γ=0 ..............(2) From eqns(1) and (2) we have α−10=β15=γ−13 or α:β:γ=10:−15:13 Substituting for α,β,γ in eqn(1) we get 10(2x+y−3)(3x+2y−7)−15(3x+2y−7)(3x+y−5)+13(3x+y−5)(2x+y−3)=0 On simplification, we get x2+y2+21x+7y−40=0