Let the locus of the midpoints of the chords of the circle x2+(y-1)2=1 drawn from the origin intersect the line x+y=1 at P and Q. Then, the length of PQ is :
- 12
- 1
- 1 2
- 2
Answer
(3) 1 2
Solution
Centre C(0,1), radius 1; O(0,0) lies on the circle
M(h,k) = mid-point of chord from O
kh k-1h=-1 h2+k2-k=0
Locus: x2+y2-y=0 (dashed circle on OC as diameter)
[figure]
With x+y=1: (1-y)2+y2-y=0 2y2-3y+1=0 y=1, 12
(0,1), Q ( 12, 12 ) = 14+ 14= 1 2
Answer: (3)