Let _1 and _2 be the radii of the largest and smallest circles, respectively, which pass through the point (-4,1) and having their centres on the…
JEE Main 2021 — Mathematics Coordinate Geometry
2021mcqmedium
Let r1 and r2 be the radii of the largest and smallest circles, respectively, which pass through the point (−4,1) and having their centres on the circumference of the circle x2+y2+2x+4y−4=0. If r2r1=a+b2, then a+b is equal to:
Official previous-year question
Held on 20 Jul 2021 · Verified 6 Jul 2026.
Options
A
3
B
11
C
5
D
7
Did you get this right?
Sign in to track your attempts and accuracy.
Solution
We have,
x2+y2+2x+4y−4=0
⇒x2+2x+1+y2+4y+4=9
⇒(x+1)2+(y+2)2=32
Centre≡(−1,−2)
CP=(−4+1)2+(1+2)2=32
Centre of smallest circle is A
Centre of largest circle is B.
r2=∣CP−CA∣=32−3
r1=CP+CB=32+3
Hence,
r2r1=32−332+3=9(32+3)2
⇒r2r1=(2+1)2=3+22
Hence,
a=3,b=2
a+b=5
Your note
Sign in to keep a private note on this question. Nothing you write is ever public.