In the face book there are many of friends on yahoo.
Yep... If you look for them, amongst the results, next to the person's picture you usually have several links. One of those is for sending a friend request. Usually, when the person has not yet decided, you can't click on that option, because you have already sent a friend request. If the person has rejected you, you can theoretically click there, because why they reject you, then it works as if you had never sent anything.
You don't idiot, you just wait!
Facebook has become one of the most widely used medium for communication all around the world. The people who are on facebook and who haven't accepted your request will not show on your facebook account. And there is no way you can find out whether they have rejected your request or are simply not connected. See the link below for reviewing Facebook policies.