1.

If the chord `xcosalpha+ysinalpha=p`of the hyperbola `(x^2)/(16)-(y^2)/(18)=1`subtends a right angle at the center, and the diameter of the circle,concentric with the hyperbola, to which the given chord is a tangent is `d ,`then the value of `d/4`is__________

Answer» Correct Answer - 24
The equation of hyperbola is
`(x^(2))/(16)-(y^(2))/(18)=1`
`"or "9x^(2)-8y^(2)-144=0`
Homogenizing this equation using
`(x cosalpha+y sin alpha)/(p)=1`
We have `9x^(2)-8y^(2)-144((x cos alpha+y sin alpha)/(p))^(2)=0`
Since these lines are perpendicular to each other, we have
`9p^(2)-8p^(2)-144(cos^(2)alpha+sin^(2)alpha)=0`
`p^(2)=144or p = pm12`
`therefore" Radius of circle"=12`
`therefore" Diameter of circle"=24`


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