Assign a value to a symbolic matrix?

Questions
1

Hi guys,
I am quite new to mathematica.
I have a simple problem, and I would like to share it with you.
suppose that I have the below matrix:

f[x_] := ( {{x*5, x^2}, {x, x - 1}  } )

now I want to assign a symbolic value to an element of the above matrix by the command below:

f[x][[2 , 2]] := x

but unfortunately mathematica says :“f[x] in the part assignment is not a symbol.”
what can I do to solve this problem,
thanks a lot

2

I’m not sure what the problem was. It works for me in 10.3.

In[1]:= $Version

Out[1]= "10.3.0 for Microsoft Windows (64-bit) (October 9, 2015)"

In[2]:= f[x_] := {{x*5, x^2}, {x, x - 1}}

In[3]:= f[x]

Out[3]= {{5 x, x^2}, {x, -1 + x}}

In[4]:= f[x][[2, 2]]

Out[4]= -1 + x

In[5]:= f[3]

Out[5]= {{15, 9}, {3, 2}}

In[6]:= f[3][[2, 2]]

Out[6]= 2