Solved: Justify the equations in either by deriving them

Chapter 9, Problem 7E

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Problem 7E

Justify the equations in either by deriving them from formulas in Example or by direct computation from Theorem Assume m, n, k, and r are integers.

Example

Values of  Think of Theorem as a general template: Regardless of what nonnegative numbers are placed in the boxes, if the number in the lower box is no greater than the number in the top box, then

Use Theorem to show that for all integers n ≥ 0,

Solution

Theorem

The number of subsets of size r (or r-combinations) that can be chosen from a set of n elements, , is given by the formula

or, equivalently

where n and r are nonnegative integers with r ≤ n.

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