Question

Can anyone tell why and where should this formula be used...plz​

Answer 1

Answer:

Step-by-step explanation:

This the formula for finding the I know that n(n+1)/2 is getting the sum of 1 to n numbers. ... Second formula can also be used to find out number of combinations how to choose two elements out of n, or how many elements Ai,j are in square matrix where i < j and probably one can find another dozen of descriptions