If y = sec(tan−1x), then dydx at x = 1 is equal to:
1√2
12
1
0
Let y=sec(tan−1x) and tan−1x=θ.⇒x=tan θ⇒y=√1+x2(∵sec2θ=1+tan2θ)⇒dydx=12√1+x2.2xAt x=1,dydx=1√2.