The product of first n positive integer, can be called as n factorial, and noted as n!
Note, the special case defined,
When we pick r objects from n objects, if the order matters, it is called as permutation, and we notate it as nPr.
If the order is unimportant, we can use combination, which is nCr.
The extra r! is the permutation in the specific set drawn out.
Note,
There will be n+1 th term.
The sum of power of x and y will equal to n.
The r+1 th term can be called as the general term, in the descending power of x.
The coefficients, r=0, 1 … are called binomial coefficients.