First slide
Equation of line in Straight lines
Question

If A and B are two fixed points, then the locus of a point which moves in such a way that the angle APB is a right angle, is  

Moderate
Solution

Let A x1 , y1 , B  x2  ,y2  be two fixed points and

let P ( h, k )  be a variable point such that  APB=π2 Then, 

Slope of AP× Slope of BP = -1

 hx1hx2+(ky/1)ky2=0

Hence, the locus of  ( h, k ) is 

 xx1xx2+yy1yy2=0 which is a circle

having  AB  as diameter

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