Find the number of ways of arranging N people in a straight line, if two particular people must always be separated.

It’s the number of ways N people can be arranged in a straight line without restriction minus the number of arrangements in which the 2 people are together.

The number of ways N people can be arranged in a straight line without restriction = N!

The number of arrangements in which the 2 people are together = the number of possible positions for the left-hand person multiplied by the number of people who can be that person, multiplied by the number of possible arrangements for the other N - 2 people

= (N - 1) * 2 * (N - 2)!

= 2 (N - 1)!

So the number of ways N people can be arranged in a straight line if 2 particular people must be separated = N! - 2(N - 1)!

50

step-by-step explanation:

not only in mathematics, scientific proof also are required in the other field of science. also maths proofs are of particular structure, containing steps and logics. so proving is like doing science, it is science. that's why it is important to prove. 

an inaccurate proof leads to errors, or stating results that are not accurate.  which wil mess the probelm up you dont want this