在微积分中,函数的任何线性组合的导数等于函数的导数的相同线性组合[ 1] ,此属性称为微分的线性(linearity of differentiation) [ 2] 、线性法则(rule of linearity)、或微分的叠加法则 [ 3] 。导数的基本属性是将两个简单的微分法则封装在一起:求和法则(两个函数之和的导数是导数的和)和常数法则(函數的常數倍的導數是該函數的導數的常數倍)[ 4] [ 5] 。因此,可以说微分作用是线性的,或者微分算子 是线性的算子[ 6] 。
設 f 和 g 為函數,同時 α 和 β 是常數,思考:
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{\displaystyle {\frac {\mbox{d}}{{\mbox{d}}x}}(\alpha \cdot f(x)+\beta \cdot g(x))}
通過微分的求和法則:
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{\displaystyle {\frac {\mbox{d}}{{\mbox{d}}x}}(\alpha \cdot f(x))+{\frac {\mbox{d}}{{\mbox{d}}x}}(\beta \cdot g(x))}
通過微分的常數法則,這一式子變為:
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{\displaystyle \alpha \cdot f'(x)+\beta \cdot g'(x)}
進而:
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{\displaystyle {\frac {\mbox{d}}{{\mbox{d}}x}}(\alpha \cdot f(x)+\beta \cdot g(x))=\alpha \cdot f'(x)+\beta \cdot g'(x)}
忽略括號,這常被寫作
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{\displaystyle (\alpha \cdot f+\beta \cdot g)'=\alpha \cdot f'+\beta \cdot g'}
^ Blank, Brian E.; Krantz, Steven George, Calculus: Single Variable, Volume 1 , Springer: 177, 2006 [2020-08-22 ] , ISBN 9781931914598 , (原始内容存档 于2021-04-29) .
^ Strang, Gilbert, Calculus, Volume 1 , SIAM: 71–72, 1991 [2020-08-22 ] , ISBN 9780961408824 , (原始内容存档 于2021-04-29) .
^ Stroyan, K. D., Calculus Using Mathematica , Academic Press: 89, 2014 [2020-08-22 ] , ISBN 9781483267975 , (原始内容存档 于2021-04-29)
^ Estep, Donald, 20.1 Linear Combinations of Functions, Practical Analysis in One Variable , Undergraduate Texts in Mathematics , Springer: 259–260, 2002 [2020-08-22 ] , ISBN 9780387954844 , (原始内容存档 于2021-04-29) .
^ Zorn, Paul, Understanding Real Analysis , CRC Press: 184, 2010 [2020-08-22 ] , ISBN 9781439894323 , (原始内容存档 于2021-04-29) .
^ Gockenbach, Mark S., Finite-Dimensional Linear Algebra , Discrete Mathematics and Its Applications, CRC Press: 103, 2011 [2020-08-22 ] , ISBN 9781439815649 , (原始内容存档 于2021-04-29) .