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If `x=9` is the chord of contact of the hyperbola `x^2-y^2=9` then the equation of the corresponding pair of tangents is (A) `9x^2-8y^2+18x-9=0` (B) `9x^2-8y^2-18x+9=0` (C) `9x^2-8y^2-18x-9=0` (D) ` `9x^2-8y^2+18x+9=0` |
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Answer» Correct Answer - 4 Let `x = 9` be the chord of contact of the given hyperbola with respect to the point `(x_(1), y_(1))`. Then its equation is given by `T=0` i.e. `x x_(1)-y y_(1)=9` `x x_(1)-y y_(1)=9` Comparing this equation to `x=9`, we get `x_(1)/1=y_(1)/0=1 implies x_(1)=1, y_(1)=0` Hence tangents are drawn from the point `(1, 0)`. So their combinaed equation is `S S_(1)=T^(2)` `(x^(2)-y^(2)-9) (-8)=(x-9)^(2)` `implies 9 x^(2)-8y^(2)-18x+9=0` |
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