How can you prove a triangle is an equilateral triangle?
A. Use the distance formula to see if at least two sides are congruent.
B. Use the slope formula to see if any sides are perpendicular.
C. Use the distance formula to see if all three sides are congruent.
D. Use the slope formula to see if any sides are parallel.
We have to use the distance formula: d = sqrt( (x2 - x1)² + ( y2 - y1 )²) When 2 sides are congruent it could be a scalene triangle, so it is not enough. All 3 sides must be congruent. Answer: C. Use the distance formula to see if all three sides are congruent.
