Tangents `P A` and `P B` are drawn to `x^2+y^2=9` from any arbitrary point `P` on the line `x+y=25` . The locus of the midpoint of chord `A B` is  `25(x^2+y^2)=9(x+y)`   `25(x^2+y^2)=3(x+y)`   `5(x^2+y^2)=3(x+y)`   `non eoft h e s e`
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