1. QTRS is a parallelogram
1. given
2. m∠T = 90°
2. given
3. ∠T ≅ ∠S
3. opp. ∠s of a parallelogram are ≅
4. m∠T = m∠S
4. def. of congruent
5. 90° = m∠S
5. substitution
6. m∠R + m∠S = 180°
6. consecutive ∠s of a parallelogram are supp. ∠s
7. m∠R + 90° = 180°
7. substitution property
8. m∠R = 90°
8. subtraction property
9. ∠R ≅ ∠Q
9. opposite ∠s of a parallelogram are ≅
10. m∠R = m∠Q
10. def. of congruent
11. 90° = m∠Q
11. substitution
12. ∠Q, ∠T, ∠R, and ∠S are right ∠s
12. def. of right angle
13. QTRS is a rectangle
13. def. of rectangle