Unfindable Hidden Partitions?

I have bought a used 2010 macbook pro 15" off of my high school, when i got it i decided to format the hard drive (500GB), and install El Capitan, but when i did this i noticed that only 274GB of it was available, there is a "recovery" partition taking up almost half of my drive. when i saw it (the first and only time) i thought nothing of it and thought that it would get wiped with the rest of the drive, but it did not. now i cannot get the debug menu to show up on the disk utility, and even terminal cannot see it. I've tried 3 or 4 different lines of code to try and fix it but none of them work, it thinks it has the debug menu, but it does not. plz help.