When you enter numbers like that, they will be converted to double precision, which does not have enough precision for you. You need to change the numbers to symbolic.
syms z
A = [1, 0; 0, ((sym('2098771722748011756657413967615')*z^2) / sym('2535301200456458802993406410752') - (sym('7700501052346207801164205137339')*z) / sym('5070602400912917605986812821504') - sym('10387006882955487611545293966533/20282409603651670423947251286016')]
