这些数学对象是抽象的，不易掌握的外行人士。
These mathematical subjects are abstract, not easy to grasp for uninitiated persons.
第二类换元法是一种既重要又不易掌握的积分方法。
The second method of transformation is an important but not-easy-to-master calculus method.
现代控制论应用状态空间方法表示，概念抽象，不易掌握。
The modern cybernetics, which is expressed by the state-space formulation, is too difficult to understand because of its abstract concepts.
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