关系定义公式FRD ？
在离子化合物中，正、负离子的比例严格遵守化学公式定义的化合价关系。
For ionic compounds, the state of having exactly the ratio of cations to anions specified by the chemical formula.
利用多元函数极值的定义和偏导数的定义公式证明二元函数与一元函数在某点取得极值的关系。
This article use the diverse function extremum and the local derivative's definition formula to prove the relation between extremum obtained by the two function and the dollar function at some point.
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