【Math】ln链式求导

ln(\frac{y}{x}) 对 x 求导的两种方法:

1. 直接链式求导:

\frac{\partial ln(\frac{y}{x})}{\partial x} = \frac{\partial ln(\frac{y}{x})}{\partial \frac{y}{x}} \frac{\partial \frac{y}{x}}{\partial \frac{1}{x}} \frac{\partial \frac{1}{x}}{\partial x} = \frac{x}{y} \cdot y \cdot (-\frac{1}{x^2}) = - \frac{1}{x}

2. 换成加法再求导:

\frac{\partial ln(\frac{y}{x})}{\partial x} = \frac{\partial (lny-lnx)}{\partial x} = \frac{\partial (-lnx)}{\partial x} = -\frac{\partial (lnx)}{\partial x} = -\frac{1}{x}

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转载自blog.csdn.net/u013541048/article/details/81584594
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