Answer:
(a) Use the distance formula to see if at least two sides are congruent
Step-by-step explanation:
You want to know how you can prove a triangle is isosceles.
Isosceles triangle
A triangle is isosceles if two sides are congruent, or if two angles are congruent. Hence one way to prove a triangle is congruent is ...
Use the distance formula to see if at least two sides are congruent, choice A.
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Additional comment
Sides of a right triangle are perpendicular. A triangle may be a right triangle without being isosceles, so showing sides are perpendicular is not helpful.
Sides of a triangle are never parallel.
While it is true that an equilateral triangle, with all sides congruent, is an isosceles triangle, the triangle may be isosceles without being equilateral.
