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Question: Answered & Verified by Expert
The slope of the line touching both the parabolas y2=4x and x2=-32y is 
MathematicsApplication of DerivativesJEE MainJEE Main 2014 (06 Apr)
Options:
  • A 1 8
  • B 2 3
  • C 1 2
  • D 3 2
Solution:
1461 Upvotes Verified Answer
The correct answer is: 1 2
y2=41x

x2=4-8y

The equation of the tangent to y2=4x is y= mx+am
The equation of the tangent to x2=4by is  y= mx-bm2

Since, they have a common tangent,

      am=-bm2

∴   1m=8m2

   m3=18

   m=12

 The slope of the common tangent is 1 2 .

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