When selecting n objects from a set of N objects, we can determine the number of experimental outcomes using permutation or combination.
When the order of selection is important, we use permutation.
However, whenever the order of selection is not important, we use combination.
Therefore, The counting rule that is used for counting the number of experimental outcomes when n objects are selected from a set of N objects where order of selection is not important is called the counting rule for combinations.
The slope of a perpendicular line is the "negative reciprocal" of the slope of the original line. so just switch the numbers and put the top number into a negative.
