this looks incorrect since xT A x is 1*1 matrix
its square is also 1*1
then we cant multiply it with x which is M*1 matrix..
so plz chek up ur question..or this may be the soln..
right, ((xT. A . x)^2) is 1*1 matrix (scaler), the scaler can be multiplied by the vector, the problem is that this scaled is a function of the unknown variable.
thanks