How Is Work Calculated in a Gas PV Diagram for Path a-d?

[Malicious]

Problem.
http://img294.imageshack.us/img294/8068/pvdiagram2fo.gif
Find Work done by each path.

My Solution.
a-b, c-d >> W=P(delta)V
a-c, b-d >> W=0

My Question.
What is the work done by the gas (path a-d)?

My Thoughts.
There is a change in both pressure and volume. However, the equation to find the work in this situation is "W=P(delta)V". There is no (delta)P.

 

[JJ420]

could anyone help him?I'm kinda interested in the answer to this as well!

 

[turdferguson]

Are you familiar with integration? The answer is always found by calculating the area under the curve, which is exactly what you did for all the other ones. In this case, the area is a trapezoid

 

[JJ420]

so the work done from a to d is W = deltaP * deltaV
very good, P is no longer constant so integrate that as well
as if it was that simple