Google Nexus 7 is preinstalled with Google Chrome browser and the default search engine on Chrome is set to Google Search. If you are big fan of Yahoo or Bing search and want any one of this to be your default search then you can follow the below mentioned steps for changing the default search engine.
Step 1: Launch Google Chrome on the Nexus 7.
Step 2: Tap the option available at the top right corner then select Settings from the menu list.
Step 3: In the Settings screen, Tap the Search engine option under Basic section.
Step 4: Now select your preferred Search engine from the list, Bing or Yahoo.
This would be made as the default search engine on Google Nexus 7.