7. Show that the dual space H' of a Hilbert space H is a Hilbert
space with inner product (', ')1 defined by
(f .. fV)1 = (z, v)= (v, z), where f.(x) = (x, z), etc.
2. (a). Prove that the sum of the two projection
operators is not a projection operator, unless the
multiplication of the two projection operators produces a zero
value.
(b). Prove that the result of the multiplication of two
projection operators is not a projection operator, unless
the two projection operators are hermitian.
Let T be a linear operator on a finite-dimensional complex
vector space V . Prove that T is diagonalizable if and only if for
every λ ∈ C, we have N(T − λIV ) = N((T − λIV
)2).
Let V be a Hilbert space. Let f(x) = ∥x∥ for x ∈ V. Using the
definition of Frechet differentiation, show that ∇f(x) = x for all
x ̸= 0. Furthermore, show that f(x) is not Frechet differentiable
at x = 0.
(a)For what range in ν is the function f(x) = x
ν
in Hilbert space? (4)
(b) Why are observables represented by Hermitian operators? Explain
fully. (3)
(c) Why are determinate states of Q eigenfunctions of Qˆ? Explain
fully. (4)
(d) Comment on the essential properties of reality, orthogonality
and completeness
for both the cases of discrete and continuous spectra.
Suppose V is a finite dimensional inner product space. Prove that
every orthogonal operator on V , i.e., <T(u),T(v)> =
<u,v>, ∀u,v ∈ V , is an isomorphism.