exact differential equation

例句：

1. 1. The math problem is so exact that it can't be solved by a calculator.
   这个数学问题太精确了，不能用计算器解决。
2. 2. The scientist used an exact measurement to ensure the results were accurate.
   科学家用精确的测量来确保结果准确无误。
3. 3. The engineer designed an exact model of the bridge to meet the specifications.
   工程师设计了一个精确的桥梁模型，以满足规格要求。