I'm teaching first semester algebra, the majority of the students share the rest of the classes. Sometimes I want to take examples from other courses so they can see that everything intertwines, but it has happend too many time that whenever I try to do that they say that they haven't study that with the corresponding teacher for whatever reason. To give a for instance, yesterday I wanted to show them that sequences could be seen as functions, but they told me that they haven't study anything about them! which is a little frightening because at this point in the semester they are suppose to know something.
When that happened at the beggining I opted to just go over what I wanted to show them in particular very quickly, but as we progress I can tell that they are falling behing way too much and fast that is also affecting my own course. At first I thought that they were exaggerating, they even told me that they geometry teacher hates them, but now the good students are failing as well. What should I do? or more over, what can be done?