Google Chrome SpeedUp test

Hi, i have this question: Recently, i run the test provided by Google-Chrome(Pagespeed Up) and after the test it shows that : Resources with a sign "?" in the URL are not saved in the cache of some caching proxy servers. Remove and encoded query string parameters in the URL for the following resources: http://latex.codecogs.com/gif.latex?... How i can remeove the sign ? or replace it in the url ?