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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`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 - B The equation of the chord of contant with respect to the point (h,k) is xh-yk=9. Comparing with x=9, we have h = 1 and k = 0 Hence, the equation of the pair of tangents through the point (1,0) is `SS_(1)=T^(2)` `rArr (x^(2)-y^(2)-9)(1^(2)-0^(2)-9)=(x-9)^(2)` `rArr -8x^(2)-8y^(2)+72=x^(2)-18x+81` `rArr 9x^(2)-8y^(2)-18x+9=0`. |
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