The formula of the surface area of a cylinder should be alphabetic

The formula of the surface area of a cylinder should be alphabetic

S=2πr²+πdh =2πr(r+h)

Letter formula of surface area of cylinder

S table = s side + s bottom x2

May I ask the following about the meaning of annuity calculation formula and symbols in the formula
If x ten thousand yuan is needed after n years and the annual rate of return is I, what is the amount to be deposited each year?
Downstairs, should it be 1 + i n power minus 1, or 1 + I (n-1) power

That's right: if you set the deposit amount as: A, there are:
A = x * I / [- 1 after the nth power of (1 + I)]

How to write the expression of the inclusion exclusion principle of four sets?

|
A1∪A2∪A3∪A4|=|A1|+|A2|+|A3|+|A4|
-|A1∪A2|-|A1∪A3|-|A1∪A4|-|A2∪A3|-|A2∪A4|-|A3∪A4|
+|A1∪A2∪A3|+|A1∪A2∪A4|+|A1∪A3∪A4|+|A2∪A3∪A4|-|A1∪A2∪A3∪A4|
The inclusion exclusion principle of N sets
|A1∪A2∪A3∪… ∪An|
=∑|Ai1|-∑|Ai1∪Ai2|+… +（-1)^(k+1)∑|Ai1∪Ai2∪… ∪Aik|
+… +（-1)^(n+1)∑|A1∪A2∪… ∪An|
Where 1 ≤ I1 ＜ I2 ＜ i(k-1)＜ik≤n