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Questions  

Let r1 and r2 be the radii of the largest and smallest circles, respectively, which pass through the point (–4, 1) and having their centers on the circumference of the circle x2+y2+2x+4y-4=0. If r1r2=a+b2, then a+b is equal to :
 

a
3
b
7
c
5
d
11

detailed solution

Correct option is C

r2=OP+r r1=OP-r r=9+9 r=3   OP=32 r1r2=OP+rOP-r=32+332-3                       =2+12-1       a+b2=3+22              a+b=2

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