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從公式開始：因變數等於常數乘以自變數 y = x + z {\displaystyle y=x+z} 然後 δ y = ( δ x ∂ ( x + z ) ∂ x ) 2 + ( δ z ∂ ( x + z ) ∂ z ) 2 = δ x 2 + δ z 2 {\displaystyle \delta _{y}={\sqrt {\left(\delta _{x}{\frac {\partial {\left(x+z\right)}}{\partial x}}\right)^{2}+\left(\delta _{z}{\frac {\partial (x+z)}{\partial z}}\right)^{2}}}={\sqrt {\delta _{x}^{2}+\delta _{z}^{2}}}}
