2.2 解答

(a) $y = \cos^{-1}{x} \Leftrightarrow x = \cos{y}$ より $1 = -\sin{y}y'$ . これを $y'$

について解くと $y' = -\frac{1}{\sin{y}}$ ． $y$

の範囲に注意して $\sin{y}$ を $x$

を用いて表わすと $\sin{y} = \sqrt{1 - \cos^{2}{y}} = \sqrt{1 - x^2}$ ．よって $y' = \frac{-1}{\sqrt{1 - x^2}}$

(b) $y = \tan^{-1}{x} \Leftrightarrow x = \tan{y}$ より $1 = \sec^{2}{y}y'$ . これを $y'$

について解くと $y' = \frac{1}{\sec^{2}{y}}$ ． $y$

の範囲に注意して $\sec^{2}{y}$ を $x$

を用いて表わすと $\cos^{2}{y} + \sin^{2}{y} = 1$ より $1 + \tan^{2}{y} = \sec^{2}{y}$ ．よって $y' = \frac{1}{1 + x^2}$

$\displaystyle{\log{y} = 2\log{x} + \frac{1}{2}\left(\log{(x^3 + 2x + 1) - \log(x^2 -3x + 1) }\right)}$

$\displaystyle{\frac{y'}{y} = \frac{2}{x} + \frac{1}{2}\left(\frac{3x^2 + 2}{x^3 + 2x + 1} - \frac{2x - 3}{x^2 - 3x + 1}\right)}$

$\displaystyle y' = x^2 \sqrt{\frac{x^3 + 2x + 1}{x^2 - 3x + 1}}\left(\frac{2}{x... ...left(\frac{3x^2 + 2}{x^3 + 2x + 1} - \frac{2x - 3}{x^2 - 3x + 1}\right)\right)$

(b)両辺に対数をとると $\displaystyle{\log{y} = \log{x^{x}} = x\log{x}}$

$\displaystyle y' = x^{x}(1 + \log{x})$

(c)両辺に対数をとると $\displaystyle{\log{y} = \log{(\sin{x})^{x} = x\log{\sin{x}}}}$

$\displaystyle y' = (\sin{x})^{x}(\log{\sin{x}} + \frac{x\cos{x}}{\sin{x}})$

(d)両辺に対数をとると $\displaystyle{\log{y} = \log{x^{1/x}} = \frac{1}{x}\log{x}}$

$\displaystyle{\frac{y'}{y} = -\frac{1}{x^2}\log{x} + \frac{1}{x}\cdot \frac{1}{x} }$

$\displaystyle y' = x^{1/x}\left(\frac{1}{x^2} - \frac{\log{x}}{x^2}\right)$

(a) $\displaystyle{\frac{dy}{dx} = \frac{dy/dt}{dx/dt}}$ より $\displaystyle{\frac{dy}{dx} = \frac{a\cos{t}}{-a\sin{t}} -\frac{\cos{t}}{\sin{t}}}$

(b) $\displaystyle{\frac{dy}{dx} = \frac{dy/dt}{dx/dt}}$ より $\displaystyle{\frac{dy}{dx} = -\frac{1 - \frac{1}{2}t^{-3/2}}{\frac{1}{2}t^{-1/2} + t^{-2}} = \frac{2t^2 - t^{1/2}}{t^{3/2} + 2}}$

$\displaystyle (x^2(1 + \sqrt{x}))^{\prime} = 2x(1 + \sqrt{x}) + x^2(\frac{1}{2\sqrt{x}}) = 2 x + \frac{5}{2} x^{3/2}$

$\displaystyle (x^3\tan{2x})^{\prime} = 3x^2 \tan{2x} + x^3(2\sec^{2}{2x}) = 2 {x^3} {{\sec^{2} (2 x)}} + 3 {x^2} \tan (2 x)$

$\displaystyle (x \sin^{-1}{x})^{\prime} = \sin^{-1}{x} + x \cdot \frac{1}{\sqrt{1 - x^2}} = \frac{x}{\sqrt{1 - {x^2}}} + \sin^{-1} (x)$

$\displaystyle (\frac{x}{x^2 + 1})^{\prime} = \frac{x^2 + 1 - x(2x)}{(x^2 + 1)^2} = \frac{1 - {x^2}}{\left( 1 + {x^2} \right)^2}$

$\displaystyle (x \sin{x})^{\prime} = \sin (x) + x \cos (x)$

$\displaystyle (x\sin^{-1}{x} + \sqrt{1 - x^2})^{\prime} = \sin^{-1}{x} + \frac{x}{\sqrt{1 - x^2}} - \frac{2x}{2\sqrt{1 - x^2}} = \sin^{-1} (x)$

$\displaystyle (\tan^{-1}{(x^2 +1)})^{\prime} = \frac{2 x}{2 + 2 {x^2} + {x^4}}$

$\displaystyle (\cos{(\sqrt{2x+1})})^{\prime} = -\frac{\sin ({\sqrt{1 + 2 x}})}{\sqrt{1 + 2 x}}$

$\displaystyle \left(\frac{\sin{x} - x\cos{x}}{x\sin{x} + \cos{x}}\right)^{\prime}$	$\displaystyle =$	$\displaystyle \frac{(\cos{x} - \cos{x} + x\sin{x})(x\sin{x} + \cos{x}) - (\sin{x} - x\cos{x})(\sin{x} + x\cos{x} - \sin{x})}{(x\sin{x} + \cos{x})^{2}}$
	$\displaystyle =$	$\displaystyle \frac{x^2}{(x\sin{x} + \cos{x})^{2}}$

$\displaystyle (e^{2x}\cos{x})^{\prime} = 2e^{2x}\cos{x} - e^{2x} \sin{x} = {e^{2 x}} \left( 2 \cos (x) - \sin (x) \right)$

$\displaystyle (\log{\vert x + \sqrt{x^2 + A}\vert})^{\prime} = \frac{1 + \frac{... ...+ A}} = \frac{\sqrt{x^2 + A} + x}{\sqrt{x^2 + A}} = \frac{1}{\sqrt{A + {x^2}}}$

(m) $\displaystyle{(\cos{\sqrt{x+ 1}})^{\prime} = -\sin{\sqrt{x+1}}(\sqrt{x+1})^{\prime} = -\frac{\sin{(\sqrt{x+1})}}{2\sqrt{x+1}}}$

(n) $\displaystyle{(e^{\sin{x}})^{\prime} = e^{\sin{x}}(\sin{x})^{\prime} = \cos{x} e^{\sin{x}}}$