Mathematics

Mathematics

Problem

Define S(x)=∫xarctan⁡x1+t4 dtS(x)=\displaystyle\int_{x}^{\arctan x} \sqrt{1+t^{4}}\,dt. Which of the following is equal to S′(x)S'(x)? a) 1+(arctan⁡x)41+x2+1+x4\dfrac{\sqrt{1+(\arctan x)^{4}}}{1+x^{2}}+\sqrt{1+x^{4}} b) 1+(arctan⁡x)41+x2−1+x41+x2\dfrac{\sqrt{1+(\arctan x)^{4}}}{1+x^{2}}-\dfrac{\sqrt{1+x^{4}}}{1+x^{2}} c) 1+(arctan⁡x)41+x2−1+x4\dfrac{\sqrt{1+(\arctan x)^{4}}}{1+x^{2}}-\sqrt{1+x^{4}} d) x1+(arctan⁡x)41+x2−1+x4\dfrac{x\sqrt{1+(\arctan x)^{4}}}{1+x^{2}}-\sqrt{1+x^{4}}

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