1. ∠A ≅ ∠D, ∠B ≅ ∠E
1. given
2. m∠A = m∠D, m∠B = m∠E
2.def. of ≅ angles
3. m∠A + m∠B + m∠C = 180
3. △ angle sum theorem
4. m∠D + m∠E + m∠F = 180
4. △ angle sum theorem
5. m∠A + m∠B + m∠C = m∠D + m∠E + m∠F
5. substitution property
6. m∠D + m∠E + m∠C = m∠D + m∠E + m∠F
6. substitution property
7. m∠C = m∠F
7. subtraction property
8. ∠C ≅ ∠F
8. def. of ≅