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求$$$\frac{d}{dx} \left(x^{\sin{\left(x \right)}}\right)$$$。
解答
設 $$$H{\left(x \right)} = x^{\sin{\left(x \right)}}$$$。
對等式兩邊取對數：$$$\ln\left(H{\left(x \right)}\right) = \ln\left(x^{\sin{\left(x \right)}}\right)$$$。
利用對數的性質改寫等式右邊：$$$\ln\left(H{\left(x \right)}\right) = \ln\left(x\right) \sin{\left(x \right)}$$$。
將等式兩邊分別微分：$$$\frac{d}{dx} \left(\ln\left(H{\left(x \right)}\right)\right) = \frac{d}{dx} \left(\ln\left(x\right) \sin{\left(x \right)}\right)$$$。
對等式左邊求導數。
函數 $$$\ln\left(H{\left(x \right)}\right)$$$ 是兩個函數 $$$f{\left(u \right)} = \ln\left(u\right)$$$ 與 $$$g{\left(x \right)} = H{\left(x \right)}$$$ 之複合 $$$f{\left(g{\left(x \right)} \right)}$$$。
應用鏈式法則 $$$\frac{d}{dx} \left(f{\left(g{\left(x \right)} \right)}\right) = \frac{d}{du} \left(f{\left(u \right)}\right) \frac{d}{dx} \left(g{\left(x \right)}\right)$$$：
$${\color{red}\left(\frac{d}{dx} \left(\ln\left(H{\left(x \right)}\right)\right)\right)} = {\color{red}\left(\frac{d}{du} \left(\ln\left(u\right)\right) \frac{d}{dx} \left(H{\left(x \right)}\right)\right)}$$自然對數的導數為 $$$\frac{d}{du} \left(\ln\left(u\right)\right) = \frac{1}{u}$$$：
$${\color{red}\left(\frac{d}{du} \left(\ln\left(u\right)\right)\right)} \frac{d}{dx} \left(H{\left(x \right)}\right) = {\color{red}\left(\frac{1}{u}\right)} \frac{d}{dx} \left(H{\left(x \right)}\right)$$返回原變數：
$$\frac{\frac{d}{dx} \left(H{\left(x \right)}\right)}{{\color{red}\left(u\right)}} = \frac{\frac{d}{dx} \left(H{\left(x \right)}\right)}{{\color{red}\left(H{\left(x \right)}\right)}}$$因此，$$$\frac{d}{dx} \left(\ln\left(H{\left(x \right)}\right)\right) = \frac{\frac{d}{dx} \left(H{\left(x \right)}\right)}{H{\left(x \right)}}$$$。
對等式右邊求導。
將乘積法則 $$$\frac{d}{dx} \left(f{\left(x \right)} g{\left(x \right)}\right) = \frac{d}{dx} \left(f{\left(x \right)}\right) g{\left(x \right)} + f{\left(x \right)} \frac{d}{dx} \left(g{\left(x \right)}\right)$$$ 應用於 $$$f{\left(x \right)} = \ln\left(x\right)$$$ 和 $$$g{\left(x \right)} = \sin{\left(x \right)}$$$：
$${\color{red}\left(\frac{d}{dx} \left(\ln\left(x\right) \sin{\left(x \right)}\right)\right)} = {\color{red}\left(\frac{d}{dx} \left(\ln\left(x\right)\right) \sin{\left(x \right)} + \ln\left(x\right) \frac{d}{dx} \left(\sin{\left(x \right)}\right)\right)}$$自然對數的導數為 $$$\frac{d}{dx} \left(\ln\left(x\right)\right) = \frac{1}{x}$$$：
$$\ln\left(x\right) \frac{d}{dx} \left(\sin{\left(x \right)}\right) + \sin{\left(x \right)} {\color{red}\left(\frac{d}{dx} \left(\ln\left(x\right)\right)\right)} = \ln\left(x\right) \frac{d}{dx} \left(\sin{\left(x \right)}\right) + \sin{\left(x \right)} {\color{red}\left(\frac{1}{x}\right)}$$正弦函數的導數為$$$\frac{d}{dx} \left(\sin{\left(x \right)}\right) = \cos{\left(x \right)}$$$：
$$\ln\left(x\right) {\color{red}\left(\frac{d}{dx} \left(\sin{\left(x \right)}\right)\right)} + \frac{\sin{\left(x \right)}}{x} = \ln\left(x\right) {\color{red}\left(\cos{\left(x \right)}\right)} + \frac{\sin{\left(x \right)}}{x}$$因此，$$$\frac{d}{dx} \left(\ln\left(x\right) \sin{\left(x \right)}\right) = \ln\left(x\right) \cos{\left(x \right)} + \frac{\sin{\left(x \right)}}{x}$$$。
因此，$$$\frac{\frac{d}{dx} \left(H{\left(x \right)}\right)}{H{\left(x \right)}} = \ln\left(x\right) \cos{\left(x \right)} + \frac{\sin{\left(x \right)}}{x}$$$。
因此，$$$\frac{d}{dx} \left(H{\left(x \right)}\right) = \left(\ln\left(x\right) \cos{\left(x \right)} + \frac{\sin{\left(x \right)}}{x}\right) H{\left(x \right)} = x^{\sin{\left(x \right)} - 1} \left(x \ln\left(x\right) \cos{\left(x \right)} + \sin{\left(x \right)}\right)$$$。
答案
$$$\frac{d}{dx} \left(x^{\sin{\left(x \right)}}\right) = x^{\sin{\left(x \right)} - 1} \left(x \ln\left(x\right) \cos{\left(x \right)} + \sin{\left(x \right)}\right)$$$A