invariant domain

例句：

1. 1. The invariant domain ofa function is the set of all valuesthat the function can take on.
   函数的不变域是函数可以取的所有值的集合。
2. 2. Invariant domains are important forstudying the behavior of functions.
   不变域对于研究函数的行为非常重要。
3. 3. The invariant domainof a polynomial is the set of allreal numbers that can be expressed as alinear combination of its roots.
   多项式的不变域是所有可以表示为其根的线性组合的实数的集合。