It is part of the optimisation tool-box. If you were using an up to date student version of Matlab it would be available. If you were using an up to date commercial version you would have had to pay extra to get the optimisation tool box and so may not have it.

Older student version of Matlab did not come with all the tool boxes (in fact it did not have most of them), Version 7 I believe fall in this category.

I don't believe you will be able to get your version to run the matlab fsolve. Octave also has fsolve, so if you cannot get a modern version of the student edition of Matlab Octave might be the best option.

CB