5. (4 pts) Prove that $[\hat{L}^2, \hat{L}_z] = 0$ using the following identities: (a) $\hat{L}^2 = \hat{L}_x^2 + \hat{L}_y^2 + \hat{L}_z^2$ (b) $[A + B + C, D] = [A, D] + [B, D] + [C, D]$ (c) $[AB, C] = A[B, C] + [A, C]B$
Added by Claire B.
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Step 1
First, let's use the identity [A+B+C,D]=[A,D]+[B,D]+[C,D] to expand [L^2,L]: [L^2,L] = [L,L]+[L,L] = 2[L,L] Show more…
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