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The locus of the point `P(h, k)` for which the line `hx+ky=1` touches the circle `x^(2)+y^(2)=4`, isA. a circleB. a parabolaC. an ellipseD. a hyperbola

Answer» Correct Answer - A
If the line `hx+ky=1` touches the circle `x^(2)+y^(2)=4`, then
`|(hxx0+kxx0-1)/(sqrt(h^(2)+k^(2)))|=2 rArr h^(2)+k^(2)=(1)/(4)`
Hence, the locus of (h, k) is `x^(2)+y^(2)=(1)/(4)`, which is a circle.


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