....................................................................... statement reason 1. angle Q congruent to angle S 1. Given angle R congruent to angle T 2. angles Q+R+S+T =360 d 2.sum of the angles theorem 3. angles R+R+S+S= 360 d 3. subsitution post. 4. angles 2R+2S = 360 d 4. addition post. 5. angles R + S = 180 d 5. div. post. 6. angles T + S = 180 d 6. subst. post. angles T + Q = 180 d angles R + Q = 180 d 7. QRST is a parallelogram 7. if the consecutive angles of a quad rilateral are supplementary the quad is a parallelogram