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JEE Main 2024
Differentiation
Differentiation
Medium

Question

Let f(x)=2x+tan1xf(x) = 2x + {\tan ^{ - 1}}x and g(x)=loge(1+x2+x),x[0,3]g(x) = {\log _e}(\sqrt {1 + {x^2}} + x),x \in [0,3]. Then

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Solution

f(x)=2+11+x2,g(x)=1x2+1f(x)=2x(1+x2)2<0g(x)=12(x2+1)3/22x<0f(x)min=f(3)=2+110=2110g(x)max=g(0)=1f(x)max=f(3)=2+tan13g(x)max=g(3)=ln(3+10)<ln<7<2\begin{aligned} & f^{\prime}(x)=2+\frac{1}{1+x^2}, g^{\prime}(x)=\frac{1}{\sqrt{x^2+1}} \\\\ & f^{\prime \prime}(x)=-\frac{2 x}{\left(1+x^2\right)^2}<0 \\\\ & g^{\prime \prime}(x)=-\frac{1}{2}\left(x^2+1\right)^{-3 / 2} \cdot 2 x<0 \\\\ & \left.f^{\prime}(x)\right|_{\min }=f^{\prime}(3)=2+\frac{1}{10}=\frac{21}{10} \\\\ & \left.g^{\prime}(x)\right|_{\max }=g^{\prime}(0)=1 \\\\ & \left.f^{\prime}(x)\right|_{\max }=f(3)=2+\tan ^{-1} 3 \\\\ & \left.g(x)\right|_{\max }=g(3)=\ln (3+\sqrt{10})<\ln <7<2 \end{aligned}

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