How can you prove a triangle is isosceles?

use the distance formula to see if at least two sides are congruent.

use the slope formula to see if any sides are perpendicular.

use the distance formula to see if all three sides are congruent.

use the slope formula to see if any sides are parallel.

The correct option is to Use the distance formula to see if at least two sides are congruent.  

Step-by-step explanation:

we know that isosceles triangle is the triangle in which two sides and two angles are equal. So, if we want to prove the triangle is isosceles we have to prove the two sides or two angles equal.

In the given options the first option is considered.

In first option only we prove at least two sides of triangle congruent by which results into two angles also congruent.

Hence, the correct option is to Use the distance formula to see if at least two sides are congruent.