Let

stand for the number of subsets of size r taken from a set of size n. (This is the number of ways of choosing r objects from n if the order does not matter.) Every subset of the set 1, 2, . . . , n either contains the element 1 or it doesn’t. By considering these two

possibilities, show that:

By using a similar method or otherwise, prove that:

I'm not sure what to do. I do not understand the queston, with what they said in the 1st paragraph and how to apply it here. Can i basically use the idea of binomial coefficients and factorials, and simplify the fraction or what?

Thanks for the help