I am getting a TypeError: unhashable type: ‘MutableDenseMatrix’ errormessage when trying to substitute values into a sympy matrix, and i am perplexed as to why

x1,x2 = symbols('x1,x2', real = true)
a,b,c,d,e,f = symbols('a,b,c,d,e,f', real = true)

x = Matrix([x1,x2])
xT = x.T

A = Matrix([[a,b],[c,d]])
b = Matrix([e,f])
qx = xT * A*x + xT*b

A = A.subs({a:2,b:-1,c:-1,d:2})

I tried substituting the values in one by one, but the b and d value never changed. Of course i expected it to substitute the values into the right places, but they never did