Express the vector R~ A B C D P R in terms of A~ , B~ , C~ , and D~ , the edges of a parallelogram. 1. R~ = C~ + D~ 2. R~ = A~ − B~ 3. R~ = A~ − C~ 4. R~ = A~ + D~ 5. R~ = B~ + D~ 6. R~ = B~ − A~ 7. R~ = A~ − D~ 8. R~ = B~ + A~ 9. R~ = D~ − A~ 10. R~ = C~ + B

Ammonia enters the expansion valve of a refrigeration system at a pressure of 10 bar and a temperature of 18oc and exits at 6.0 bar. the refrigerant undergoes a throttling process. determine the temperature, in oc, and the quality of the refrigerant at the exit of the expansion valve.