SOLUTION: A, B, C, and D are four points on the plane such that any three of them are not on the same straightness. How many straight lines can be drawn between any two of these points?
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-> SOLUTION: A, B, C, and D are four points on the plane such that any three of them are not on the same straightness. How many straight lines can be drawn between any two of these points?
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Question 1107154: A, B, C, and D are four points on the plane such that any three of them are not on the same straightness. How many straight lines can be drawn between any two of these points? Answer by ikleyn(52781) (Show Source):
Under the given condition, each line corresponds to each pair of different points by an unique way.
Hence, the number of different lines is the same as the number of different pairs of points, which is equal
to the number of combinations of 4 items taken 2 at a time: = = 6.
Note that the order of the points in pairs does not matter.
Therefore, we consider COMBINATIONS, not permutations.
