In some cases, you may have a list of numbers with a missing term in the middle. Begin, as before, by checking that your list is an arithmetic sequence. Select any two consecutive terms and find the difference between them. Then check this against two other consecutive terms in the list. If the differences are the same, you can presume that you are working with an arithmetic sequence and proceed. For example, suppose you have the list 0,4{\displaystyle 0,4},___,12,16,20{\displaystyle 12,16,20}…. Start by subtracting 4−0{\displaystyle 4-0} to find a difference of 4. Check this against two other consecutive terms, such as 16−12{\displaystyle 16-12}. The difference is again 4. You can proceed. This is similar to adding a term to the end of a sequence. Find the term that immediately precedes the space in your sequence. This is the “last” number that you know. Add your common difference to this term, to find the number that should fill in the space. In our working example, 0,4{\displaystyle 0,4},____,12,16,20{\displaystyle 12,16,20}…, the term preceding the space is 4, and our common difference for this list is also 4. So add 4+4{\displaystyle 4+4} to get 8, which should be the number in the blank space. To be sure that you have the correct answer, check from the other direction. An arithmetic sequence should be consistent going in either direction. If you move from left to right and add 4, then going in the opposite direction, from right to left, you would do the opposite and subtract 4. In the working example, 0,4{\displaystyle 0,4},___,12,16,20{\displaystyle 12,16,20}…, the term immediately following the space is 12. Subtract the common difference of 4 from this term to find 12−4=8{\displaystyle 12-4=8}. The result of 8 should fill in the blank space. The two results that you get, from adding up from the bottom or from subtracting down from the top should match. If they do, then you have found the value for the missing term. If they do not, then you need to check your work. You may not have a true arithmetic...

How would you rephrase that briefly using Chinese?
首先检查是否是等差数列。 用公差加上空格前的那一项。 用空格后的数字减去公差。 比较结果。