To complete Alfred's argument, we can fill in the blanks as follows:
- Suppose triangle ABC is congruent to triangle DEF.
- Then there is a series of rigid motions that maps triangle ABC onto triangle DEF.
- Any rigid motion of a triangle preserves the distances between every pair of corresponding points in the triangle.
- Therefore, if two triangles are congruent, then corresponding angles have equal measures and corresponding sides have equal lengths.
So, the filled-in argument reads:
- Suppose triangle ABC is congruent to triangle DEF.
- Then there is a series of rigid motions that maps triangle ABC onto triangle DEF.
- Any rigid motion of a triangle preserves the distances between every pair of corresponding points in the triangle.
- Therefore, if two triangles are congruent, then corresponding angles have equal measures and corresponding sides have equal lengths.