What should I do if the series encounters the problems of splitting item cancellation and dislocation subtraction? Where to start?

I haven't done series for a long time. I was more interested in series in high school. It happens that my old class is a math teacher, and the progression is very clear, so I understand it.

The elimination of split terms should be the kind that will eventually be reduced to a regular score MINUS a score. The initial problem is the relationship between the denominators of two terms. You can add and subtract to see what the law is, and some need to multiply a number to make the molecule one, so you can find the law and solve it.

Dislocation subtraction is the sum of arithmetic multiplication and equal proportion. You need to list the first three items, find the rules, and then write an and An+ 1. Because you need to multiply q when writing, you should pay attention to alignment when writing An+ 1 Alignment is the key.

Alignment, if An is one, then An+ 1 multiplied by q needs to be written under the second item of An, and it is best to write it in detail with a big piece of grass paper, and gradually get used to writing the first three items, the last three items and the middle. The first three items are easy to understand, and the last three items are to eliminate the same item. Of course, the last item cannot be ruled out. Subtract and you get the result.

Ps: Here, An refers to sum, that is, the sum of the first n terms of an, an=bn×cn, where bn is arithmetic and cn is proportional.

If you don't know my classmates, you can add a specific topic to let me know, or add my Baidu account to find me ... There are also people with strong math skills around me ~ In fact, I am a little better than the series, and everything else is OK. I don't like calculus. It's hard to die. ...