7-2  ʹsyműʽ 
⣺Ȳõ巨Enterȷϡ
>> a = sym('a');
>> b = sym('b') ;
>> c = sym('c');
>> x = sym('x');

>> f=a*x^2 + b*x + c
f =
a*x^2+b*x+c
>> 
