Question

Can anyone help me to solve the problem about quantum physics? The variance σX2=⟨(X^−⟨X^⟩)2⟩ of an operator, X^, is a measure of how large a range its possible values are spread over (the standard deviation is given by σ=σ2). Suppose that |X⟩ is an eigenstate of some operator X^, what is the variance of X^ in this state? You may assume that |X⟩ is normalized (⟨X|X⟩=1). Note that the expectation value of an operator in the state |ψ⟩ is given by ⟨O^⟩≡⟨ψ|O^|ψ⟩.