 # let P is variable point on line Y=4.tangents are drawn to circle x²+y² =4 from P touching circle at A and B.if parallelogram PAQB is completed the prove that locus of Q will be (y+4)(x² +y²)=2y² Badiuddin askIITians.ismu Expert
148 Points
13 years ago

Dear piyush chord of contact of circle from P is

ax +4y =4 .............1

equation of chord bisected at a point O is

x(a+h)/2  + y (k+4)/2 -4 = {(a+h)/2}2  + {(k+4)/2} -4

x(a+h)/2  + y (k+4)/2  = {(a+h)/2}2  + {(k+4)/2}  ....................2

equation 1 and 2 represent same line AB so

(a+h)/2a   = (k+4)/2*4    =  [{(a+h)/2}2  + {(k+4)/2}2  ]/4

so  (a+h)/2a   = (k+4)/2*4

1+ h/a  = k/4 +1

a = 4h/k

and   (k+4)/2*4    =  [{(a+h)/2}2  + {(k+4)/2}2  ]/4

( k+4)/2    =    {(4h/k+h)/2}2  + {(k+4)/2}2

( k+4)/2    =    {(4h/k+h)/2}2  + {(k+4)/2}2

( k+4)/2    =   h2/k2 {(k+4)/2}2  + {(k+4)/2}2

(k+4)(h² +k²)=2k²

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