Let the latus rectum of the hyperbola x^2 9- y^2 b^2=1 subtend an angle of π 3 at the centre of the hyperbola. If b^2 is equal to m(1+√n), where l…
JEE Main 2024 — Mathematics Coordinate Geometry
2024integermedium
Let the latus rectum of the hyperbola 9x2−b2y2=1 subtend an angle of 3π at the centre of the hyperbola. If b2 is equal to ml(1+n), where l and m are co-prime numbers, then l2+m2+n2 is equal to __________.
Official previous-year question
Held on 30 Jan 2024 · Verified 6 Jul 2026.
Did you get this right?
Sign in to track your attempts and accuracy.
Solution
Given,
Equation of hyperbola 9x2−b2y2=1
And latusrectum LR subtends 60∘ at centre
Now, plotting the diagram we get,
Now, from above diagram we get A(ae,\frac{{b}^{2}}{a})&B(ae,\frac{-{b}^{2}}{a})
⇒tan30∘=aeab2=a2eb2=31
⇒e=93b2as a2=9
Also, e2=1+9b2
⇒1+9b2=813b4
⇒b4=3b2+27
⇒b4−3b2−27=0
⇒b2=23+117 {ignoring the negative sign as it is a square function}
⇒b2=23(1+13)
Hence, on comparing with ml(1+n) we get,
⇒l=3,m=2,n=13
⇒l2+m2+n2=182
Your note
Sign in to keep a private note on this question. Nothing you write is ever public.