Circulation over a triangle in R^3

[sriracha]

I have attached a file with all needed information including the function and path of integration. My work seems right to me, but the correct answer is a^2. Will someone please take a look and show me where my misstep is.

 

[sriracha]

Just to be sure, can someone confirm the file opens/ is legible?

 

[Borek]

Yes it opens.

 

[sriracha]

thanks