http://www.texify.com/img/\normalsize\!\langle\hat A\rangle.gif is the expectation value of http://www.texify.com/img/\normalsize\!\langle\hat A\rangle.gif

I don't know what means expectation value of an opertor, square of an operator and square of all items texify.com/img/\LARGE\!\langle\hat A\rangle^2\, \langle\hat A^2\rangle.gif