1.

The foci of a hyperbola are `(-5,18)` and `(10,20)` and it touches the `y`-axis . The length of its transverse axis, isA. `100`B. `sqrt(89)//2`C. `sqrt(89)`D. `sqrt(50)`

Answer» Let `2a` and `2b` be respectively lengths of transverse and conjugate axes of the hyperbola and its eccentricity be `e`.
Then,
`2ae="Distance between foci"=2ae=17impliesae=(17)/(2)`
We know that the product of lengths of perpendicular from two foci on any tangent to a hyperbola is `b^(2)`. Since given hyperbola touches `y`-axis i.e., `x=0`
`:.b^(2)=50`
`impliesa^(2)(e^(2)-1)=50implies(289)/(4)-a^(2)=50impliesa^(2)=(89)/(4)impliesa=(sqrt(89))/(2)`
Hence, length of transverse axis `=2a=sqrt(89)`.


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