Let A( , 0) and B(0, ) be the points on the line 5 x+7 y=50. Let the point P divide the line segment A B internally in the ratio 7: 3. Let 3 x-25=0 be a directrix of the ellipse E: x2a2+ y2b2=1 and the corresponding focus be S. If from S, the perpendicular on the x-axis passes through P, then the length of the latus rectum of E is equal to,
- 253
- 259
- 325
- 329
Answer
(3) 325
Solution
A(10, 0), B (0, 507 ) P= ( 7 0+3 1010, 7 507+3 010 )=(3, 5)
[figure]
∵ SP x-axis S =(3, 0) ae=3
Directrix 3x-25=0 ae= 253
a2=ae ae=25 a=5, e= 35
b2=a2(1-e2)=25-9=16
latus rectum = 2b2a= 325
Answer: (3)