What you’ll learn
Use SSS.
Key idea
SSS uses all three corresponding side lengths; rotation or reflection does not change them.
All three corresponding sides suffice regardless of orientation; each perimeter uses every side once.
Worked example
Enter the exact value or ordered values in the format requested below.
Triangle ABC: AB=2, BC=7, AC=7; correspondence A-D, B-E, C-F. DEF has DE=2, EF=7, DF=7. Use SSS and find DEF perimeter.
- Corresponding sides DE=2, EF=7, DF=7 satisfy SSS with a realizable strict triangle.
- Perimeter is 2+7+7=16; DF matches AC=7, regardless of orientation.
Answer: 16
Quick Check
Evaluate a worked attempt at use sss, identify the first invalid step, and provide the correction.
Triangle ABC: AB=4, BC=2, AC=3; correspondence A-D, B-E, C-F. DEF has corresponding lengths 4,2,3. Student: Step 1, all three side pairs match. Step 2, the triangles need not be congruent because one is reflected. Identify first invalid step and correct conclusion and perimeter.