# Some algebra

1. Dec 15, 2008

### koolmodee

We have f(E)q(-E) + f(-E)q(E)

now change to x(E)=q(E) + f(E)/ (term)

and get -(f(E)f(-E))/(term)

I plugged the changed variable in, but didn't get the result, any hints how to proceed?

I got that from page 63, 64 equations 7.6, 7.7, 7.8 from this text: http://www.physics.ucsb.edu/~mark/ms-qft-DRAFT.pdf

thank you

2. Dec 15, 2008

### HallsofIvy

Staff Emeritus
?? 7.6, 7.7, and 7.8 are nothing like what you give here! 7.6 involves an integral and "x" is a change of variable in the integral.

3. Dec 15, 2008

### gabbagabbahey

Just rearrange your variable substitution to isolate $q(E)$, and then determine $q(-E)$, and substitute into equation (7.6) and simplify.

No offense, but this should be pretty straightforward for someone who's studying QFT.