Q.

Let the foci of a hyperbola be (1, 14) and (1, –12). If it passes through the point (1, 6) then the length of its latus-rectum is :          [2025]

1 256  
2 245  
3 1445  
4 2885  

Ans.

(4)

Distance between foci (11)2+(14+12)2

 2be=26  be=13

Mid-point of foci =(1+12,14122)=(1,1)

Equation of hyperbola is (x1)2a2+(y1)2b2=1

Hyperbola passes through (1, 6)

  (61)2b2=1  b2=25

Now, a2=b2(e21)=b2e2b2=16925=144

  a2=144 and b2=25

   Length of latus rectum =2a2b=2×1445=2885