∑ is a simple symbol of summation of series, followed by k 2 is a general term formula, the following k= 1 is the number of terms at the beginning of the initial term, and the above n is the number of terms at the end.

n

∑k^2= 1^2+2^2+……+n^2……( 1)

k= 1

n

∑(2k+ 1)= 3+5+……+(2n+ 1)……(2)

k= 1

Then (1)+(2)= 1

n

∑(k+ 1)^2=2^2+3^2+……+(n+ 1)^2

k= 1

The extension of the famous binomial theorem can be expressed as

n

∑C(n,k)a^(n-k)b^k.

k=0