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## Main Question or Discussion Point

hey, can someone show me the step between these two lines of equations please:

[tex](\Delta A)^2=<\psi|A^2|\psi>-<\psi|A|\psi>^2[/tex]

[tex]=<\psi|(A-<A>)^2|\psi>[/tex]

where A is an operator and [tex]\psi[/tex] is the wavefunction and [tex]<A>[/tex] is the expectation value of A

[tex](\Delta A)^2=<\psi|A^2|\psi>-<\psi|A|\psi>^2[/tex]

[tex]=<\psi|(A-<A>)^2|\psi>[/tex]

where A is an operator and [tex]\psi[/tex] is the wavefunction and [tex]<A>[/tex] is the expectation value of A