When there is little difference between the maximum size and the minimum size, it is often classified by arithmetic progression.

If it is arithmetic progression, and there are AP = q and AQ = p, then a (p+q) =-(p+q).

If it is arithmetic progression, and an = m and am = n, then a (m+n) = 0.

2. A series of problems in mortgage repayment

With the active promotion of the central government

, buy

Payment for goods (

The introduction of this system has greatly stimulated people's

, expanded.

, effectively pull

.

As we all know, mortgage payment (

) implemented on a monthly basis.

. It is often difficult for people to know how this equal amount is obtained and how much principal should be returned to the bank in a few months. Let's find a solution to this problem.

If the loan amount is a0 yuan, the loan

P, the repayment method is monthly.

One yuan. Let the principal after repayment in the nth month be an, and then there are:

a 1=a0( 1+p)-a，

a2=a 1( 1+p)-a，

a3=a2( 1+p)-a，

......

an+ 1=an( 1+p)-a，.........................(*)

Convert (*) into (an+1-a/p)/(an-a/p) =1+p.

Therefore, {an-a/p} is an item with a 1-a/p as the head and 1+p as the common ratio.

. All problems related to mortgage payment in daily life can be calculated according to this formula.