1.

Two rods of lengths a and b slide along the axes in such a way that their ends are concyclic. The locus of the centre of the circle passing through these points is

Answer»

`4(x^(2)+y^(2))=a^(2)+b^(2)`
`x^(2)-y^(2)=a^(2)-b^(2)`
`4(x^(2)-y^(2))=a^(2)-b^(2)`
`x^(2)-y^(2)=a^(2)+b^(2)`

Solution :Let `A_(1)A_(2) and B_(1)B_(2)` be two rods of length a and b which slide LONG OX and OY respectively.
Let `x^(2) + y^(2) +2gx +2fy +c= 0` be the circle passing through `A_(1), A_(2), B_(1), B_(2)`.Then
`A_(1)A_(2)`= Intercept of x-axis `=2 sqrt(g^(2)-c)`
`rArr a=2 sqrt(g^(2)-c)`...(i)
`B_(1)B_(2)`= intercept of y-axis
`2sqrt(f^(2)-c)`...(ii)
Squaring (i) and (ii), we get
`a^(2)=4(g^(2)-c)`
`b^(2)=4 (f^(2)-c)`
Substracting `a^(2)-b^(2)=4(g^(2)-f^(2))`
HENCE locus of CENTRE is `a^(2)-b^(2)=4(x^(2)-y^(2))`


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