Why does equation 35.21 have an extra minus sign?

[sunshine9]

TL;DR

Hi,everybody,I'm reading Srednicki's qft textbook,and I'm puzzled by the calculation about spinor indices.I can't realize Eq35.21.

Eq35.17 and 35.18 is obtained,but the result of Eq35.21 I obtained has an extra minus sign,I don't know what's wrong of my calculation,so I hope some people much more smarter can figure it out.Thanks.

 

[azntoon]

The minus sign in equation 35.21 is most likely due to a mistake in the algebraic manipulation of the equation. You can try double-checking your work to see if you can spot where the error is, or you can try consulting with someone else who is better at algebra to help you find the mistake.