Cartersian double integral converted to polar and then evaluated #2

[jimbo71]

Homework Statement

convert line one to polar integral and then evaluate
see problems 16 attachement

Homework Equations

r^2=y^2+x^2

The Attempt at a Solution

I changed to polar and evaluated the double integral but I come up with an answer of negative pi which seems odd since it is an area value and should be posititve. What did i do wrong?
see problem 16 attachement

 

[quantumdude]

You made a careless sign error at the start of the 4th line. There should be a negative in front of the integral in that step.