1. Starting from the basics: First, relearn the basic knowledge of high school mathematics, such as algebra, geometry and trigonometric functions. You can learn this knowledge by consulting textbooks, reference books or online resources.

2. Make a study plan: In order to ensure the systematicness and continuity of study, it is necessary to make a detailed study plan. The plan should include daily study time, study contents and objectives, and weekly review and summary.

3. Do more exercises: The core of mathematics learning is a large number of exercises. By doing problems, we can deepen our understanding of knowledge points and improve our ability to solve problems. You can change from easy to difficult, gradually increase the difficulty and constantly challenge yourself.

4. Review and consolidate in time: While learning new knowledge, we should review old knowledge in time and consolidate what we have learned. You can review by doing exercises after class, participating in class discussions or asking questions with your classmates.

5. Ask for help: When you encounter difficulties in your study, don't be afraid to ask for help. You can ask the teacher for advice, or join a study group to discuss this problem with your classmates. In addition, you can also use network resources, such as online education platforms and learning forums, to find solutions and learning methods.

6. Develop good study habits: It is very important to develop good study habits to improve the learning effect. Stay focused and avoid distractions; Arrange time reasonably to ensure adequate rest; Keep a positive attitude and believe that you can overcome difficulties.

7. Take the mock exam: By taking the mock exam, you can test your academic performance and know what you need to strengthen. At the same time, mock exams can also exercise the ability to take exams and make full preparations for the college entrance examination.

In a word, the key to make up for the poor math foundation in senior three lies in finding suitable learning methods, persistent study and practice, and gradually improving their math level.