These are declaring variables of those names, hiding the functions that you are trying to call. (I think that's what Peter87 is hinting at.)
Also, vlad is correct--you have type mismatches in your perimeter function. When you fix the first error, you will run into this one.
By the way, when you post code, please put it inside code tags. Click the "<>" button in the Format menu and past your code between the tags. I makes it easier to read, and it gives line numbers, making it easier to make comments about.