matlab代码问题求助

初学matlab，R2010b的版本，写了这么一段
f=@(x)5*x^2

f =

     @(x)5*x^2

>> g=quad(@(x)f(x),2,4)
??? Error using ==> mpower
Inputs must be a scalar and a square matrix.

Error in ==> @(x)5*x^2


Error in ==> @(x)f(x)


Error in ==> quad at 77
y = f(x, varargin{:});

这是为啥子咧

f=@(x)5.*x.^2;
>> g=quad(f,2,4)

g =

   93.3333