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Conditions for the existence of mathematical expectation
Absolute convergence of conditional integral for existence of mathematical expectation.

First of all, mathematical expectations

In probability theory and mathematical statistics, mathematical expectation (or mean, also known as expectation) is the sum of the probabilities of each possible result multiplied by its result in the experiment, and it is one of the most basic mathematical characteristics. It reflects the average value of random variables.

It should be noted that the expected value is not necessarily equal to the common sense "expectation"-"expected value" is not necessarily equal to every result. The expected value is the average of the output values of variables. The expected value is not necessarily contained in the set of output values of variables. The law of large numbers shows that as the number of repetitions approaches infinity, the arithmetic mean of numerical values almost inevitably converges to the expected value.

Second, math skills.

1, part of improving math scores

I may have studied mathematics for a while, but I always fail in my grades. What is the difference? Basic questions or high questions, and then set high requirements for yourself, strive for the basic questions without losing points, and then do some difficult questions.

2. Follow the book to do exercises

Preview is not an end. If you have time, you can do examples and exercises after class and check the preview. If you can explain everything, you can learn it. Even if you can't, you can listen to the teacher again.

3. Do the homework assigned by the teacher and do it carefully.

Mathematics focuses on understanding. When you begin to learn knowledge, you must understand it. So listen carefully in class and see how the teacher explains it. When you do it, you can write the problem-solving process directly next to the topic, such as multiple-choice questions and fill-in-the-blank questions, because there are many blanks to write in the solution. The advantage of this is that the teacher can keep up with the ideas when talking about the topic, and it is not easy to get distracted.

Step 4 sort out the wrong questions

After every exam, there are always many wrong questions. For these questions, don't think that you will do them if you understand them in class. It's easier to see flowers than to embroider. You will know if you can do it yourself. Moreover, we should refer to the wrong questions in the reference book and re-learn the knowledge.