Use the distance formula to calculate the length of all three sides, and check whether all sides are congruent.
Step-by-step explanation:
An equilateral triangle would have three sides that are all the same length, out of these options, only using the distance formula to calculate the length of all three sides and checking whether they are all congruent will make sure that the triangle is equilateral instead of just isosceles.
it is a rational number.