Final answer:
An indirect proof can be used to prove that no two altitudes of a scalene triangle are congruent.
Step-by-step explanation:
An indirect proof can be used to prove that no two altitudes of a scalene triangle are congruent.
Assume that there are two altitudes of a scalene triangle that are congruent.
By definition, an altitude is a perpendicular line segment drawn from a vertex of a triangle to the opposite side.
In a scalene triangle, no two sides are congruent, so if two altitudes are congruent, then the two sides they are drawn from must be congruent as well, which contradicts the definition of a scalene triangle.
Therefore, our assumption that there are two congruent altitudes is false.
As a result, we can conclude that no two altitudes of a scalene triangle are congruent.