Question
If a tangent of slope 2 of the ellipse x2a2+y2b2=1 is normal to the circle x2+y2+4x+1=0 then the maximum value of ab is
Answer: Option B
:
B
A tangent of slope 2 is y=2x±√4a2+b2 ,this is normal to x2+y2+4x+1=0
then 0=−4±√4a2+b2⇒4a2+b2=16
usingA.M.≥G.M.,Wegetab≤4
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:
B
A tangent of slope 2 is y=2x±√4a2+b2 ,this is normal to x2+y2+4x+1=0
then 0=−4±√4a2+b2⇒4a2+b2=16
usingA.M.≥G.M.,Wegetab≤4
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