JEE Main 2016 · 3 April · Mathematics · Limits
A. 12\dfrac{1}{2}21
Let P=(1+tan2x)12x(1∞P = \left(1 + \tan^{2}\sqrt{x}\right)\dfrac{1}{2x} ( {1}^{\infty}P=(1+tan2x)2x1(1∞ form)))
If l=limx→a[f(x)]g(x),l = \lim_{x \to a}{\left[f\left(x\right)\right]}^{g\left(x\right)},l=limx→a[f(x)]g(x), where limx→af(x)→1\lim_{x \to a}f\left(x\right) \to 1limx→af(x)→1 and limx→ag(x)→∞,\lim_{x \to a}g\left(x\right) \to \infty ,limx→ag(x)→∞, then
l=elimx→a[f(x)−1]⋅g(x)l = {e}^{\lim_{x \to a}\left[f\left(x\right) - 1\right] \cdot g\left(x\right)}l=elimx→a[f(x)−1]⋅g(x)
⇒P=elimx→0+(1+tan2x−1)⋅12x⇒ P = {e}^{\lim_{x \to {0}^{+}}\left(1 + \tan^{2}\sqrt{x} - 1\right) \cdot \dfrac{1}{2x}}⇒P=elimx→0+(1+tan2x−1)⋅2x1
⇒P=elimx→0+12(tanxx)2⇒ P = {e}^{\lim_{x \to {0}^{+}}\dfrac{1}{2}{\left(\dfrac{tan\sqrt{x}}{\sqrt{x}}\right)}^{2}}⇒P=elimx→0+21(xtanx)2
Using limx→0(tanxx)=0,\lim_{x \to 0}\left(\dfrac{\tan x}{x}\right) = 0,limx→0(xtanx)=0, we get
P=e12P = e\dfrac{1}{2}P=e21
⇒logP=log(e12)=12⇒ logP = \log \left(e\dfrac{1}{2}\right) = \dfrac{1}{2}⇒logP=log(e21)=21.