1.

A point P moves on x-y plane such that PS +PS' = 4 where S(K,0) and S'(-K,0), then which of the following is not true about the locus of P?

Answer»

ellipse if `K in (-2,2)`
pair of coincidence lines if `K = +-2`
empty if `K in (-oo,-2) UU(2,oo)`
NONE of these

Solution :If PSS' forms a TRIANGLE, then ellipse
`:. PS + PS' gt SS'`
`RARR K in (-2,2)`
If PSS' is collinear, the pair of coincident lines `rarr K = +-2`
If PSS' neither forms triangle nor collinear then empty set
`rArr PS + PS^(1) lt SS^(1)`
`rArr K in (-oo,-2) uu(2,oo)`


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