fzero() cannot be used with two equations or two unknowns.
fsolve() from the Optimization toolbox can be used.
Also, fminsearch() from basic MATLAB can be used, if you rewrite in terms of the square of the function -- in which case the minima of the square would be when the function was zero. However, it is difficult to use fminsearch() with constraints. But in the File Exchange you can find John D'Errico's fminsearchbnd to do an fminsearch with upper and lower bounds.
