Distance formula is a the key element in the proof of the triangle inequality theorem. Option D is correct.
Distance formula is key element in which of the following is to be determine.
Distance formula used to evaluate distance between two coordinates.
Here, CPCTC, the low of sine and the low of cosines Distance formula is not necessary to prove these theorems. But in triangle inequality theorem the distance formula play major key role. In triangle inequality Distance of one side should be less than sum of distance of other two sides.
Thus, distance formula is a the key element in the proof of the triangle inequality theorem.
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