ddx1+x2=\dfrac{d}{dx}\sqrt{1 + x^2} =dxd1+x2=A11+x2\dfrac{1}{\sqrt{1+x^2}}1+x21Bx1+x2\dfrac{x}{\sqrt{1+x^2}}1+x2xcheck_circleC2x1+x2\dfrac{2x}{\sqrt{1+x^2}}1+x22xD121+x2\dfrac{1}{2\sqrt{1+x^2}}21+x21Explanation121+x2⋅2x=x1+x2\dfrac{1}{2\sqrt{1+x^2}} \cdot 2x = \dfrac{x}{\sqrt{1+x^2}}21+x21⋅2x=1+x2x.