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1)

If y=sec(tan1x)   then dydx  at x=1 is equal to 


A) 12

B) 12

C) 1

D) 2

Answer:

Option A

Explanation:

Given , y= sec {tan-1   x)

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   Let   tan1x=θx=tanθ

        y=secθ=1+x2

  On differentiating w.r.t x, we get

        dydx=121+x22x

   At x=1,    dydx=12