With variable substitution, several kinds of linear differential equations are solved and several sufficient and necessary conditions are obtained.

借助于变量代换，求解几类线性微分方程，并得到了几个求解的充分必要条件。

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A mathematics model which deals with 54 variables and 43 constraint conditions is proposed to optimize the product structure by using linear programming theory.

本文运用线性规划理论，建立了一个包括54个变量(产品)，43个约束条件产品结构优化数学模型。

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The general inference and demonstration of the equilibrium problem of particle system are carried on, the full and necessary conditions are given while the constraint is ideal, linear and scleronomic.

本文就质点系平衡问题进行了一般性的推证，给出了当约束是理想、线性定常约束时的质点系平衡的充要条件。

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Yet we continue to operate as if we can magically superimpose control, accurate long-range forecasts, accurate budget projections, ever-increasing performance arrows and other products of strictly linear thinking on those complex and interwoven conditions beyond our four walls and that, somehow, it will all work out just as planned.

FORBES: Throw Out Your Plans for 2013. Business Is a Journey.