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BITSAT2013MathematicsCircleActual

A pair of tangents are drawn from the origin to the circle x²+y²+20(x+y)+20=0, then the equation of the pair of tangent are

Options

  1. Ax²+y²-5 x y=0
  2. Bx²+y²+2 x+y=0
  3. Cx²+y²-x y+7=0
  4. D2 x²+2 y²+5 x y=0

Correct answer

D. 2 x²+2 y²+5 x y=0

Step-by-step solution

Equation of pair of tangents is given by SS ₁= T ² array l or S = x ²+ y ²+20( x + y )+20, ~S ₁=20 ~T =10( x + y )+20=0 SS ₁= T ² 20 ( x ²+ y ²+20( x + y )+20 )=10² ( x + y +2)² 4 x ²+4 y ²+10 xy =0 2 x ²+2 y ²+5 xy =0 array

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